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Gemmology2008 / Volume 31 / Nos. 3/4

The Gemmological Association of Great Britain

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President: Professor A. H. Rankin Vice-Presidents: N. W. Deeks, R. A. Howie Honorary Fellows: R. A. Howie, K. Nassau Honorary Life Members: H. Bank, T.M.J. Davidson, D. J. Callaghan, E. A. Jobbins, J. I. Koivula, M.J. O'Donoghue, C. M. Ou Yang, I. Thomson, V. P. Watson, C. H. Winter Chief Executive Officer: J. M. Ogden Council: A. T. Collins – Chairman, S. Collins, J. Riley, E. Stern, J. F. Williams Members’ Audit Committee: A. J. Allnutt, P. Dwyer-Hickey, J. Greatwood, G. M. Green, B. Jackson, D. J. Lancaster Branch Chairmen: Midlands – P. Phillips, North East – M. Houghton, North West – J. Riley, Scottish – B. Jackson, South East – V. Wetten, South West – R. M. Slater

The Journal of Gemmology

Editor: Dr R. R. Harding Assistant Editors: M. J. O’Donoghue, P. G. Read Associate Editors: Dr A. J. Allnutt (Chislehurst), Dr C. E. S. Arps (Leiden), G. Bosshart (Horgen), Prof. A. T. Collins (London), J. Finlayson (Stoke on Trent), Dr J. W. Harris (Glasgow), Prof. R. A. Howie (Derbyshire), E. A. Jobbins (Caterham), Dr J. M. Ogden (London), Prof. A. H. Rankin (Kingston upon Thames), Dr K. Schmetzer (Petershausen), Dr J. E. Shigley (Carlsbad), Prof. D. C. Smith (Paris), E. Stern (London), Prof. I. Sunagawa (Tokyo), Dr M. Superchi (Milan) Production Editor: M. A Burland The Editor is glad to consider original articles shedding new light on subjects of gemmological interest for publication in The Journal of Gemmology. A Guide to the preparation of typescripts for publication in The Journal is given on our website, or contact the Production Editor at the Gemmological Association of Great Britain. Any opinions expressed in The Journal of Gemmology are understood to be the views of the contributors and not necessarily of the publishers.

A fancy reddish brown diamond with new optical absorption features

Taijin Lu, Tatsuya Odaki, Kazuyoshi Yasunaga and Hajime Uesugi

Abstract: Red or near-red natural diamonds are extremely rare, and the possible origins of their colour are unclear. A weak absorption band at 776 nm in the visible range and a clear absorption band at 6169 cm-1 in the infrared region were detected in a near-red diamond, which could be factors in understanding the possible origin of this colour in natural diamonds. Keywords: diamond, spectroscopy, infrared, photoluminescence, UV-visible

Introduction red are among the most intriguing and spectra were recorded with a Nihonfenko Although the popular image of highly valued gems in the world, because high-resolution spectrometer (Model diamond for centuries has been that of a of both the richness of their colour and Jasco V-670, 300 – 1000 nm, 0.5 nm colourless gem, it can be yellow, orange, their extreme rarity. As stated by the resolution, deuterium-tungsten-halogen blue, green, black, white, purple, pink Gemological Institute of America (GIA), source) with our own designed optical and red, colours which are traditionally until 2002 only four fancy red diamonds ﬁ bre system which allows us to record referred to as ‘fancy’ (see, e.g., Fritsch, from the public domain had been graded the spectra at liquid nitrogen temperature 1998). Coloured diamonds contain in the GIA Gem Laboratory (King and with high resolution. Infrared absorption impurities, such as nitrogen or boron, or Shigley, 2003). The diamonds with near- spectra were collected using both the structural defects, and are usually graded red colours are usually graded using Nihonfenko Jasco FT/IR-6100 and the FT/ using a fancy-colours grading system additional descriptive terms, such as IR-660 plus Fourier-transform infrared (King et al., 1994). In this system, the fancy purple-pink, fancy reddish purple, (FTIR) spectrometers (6,000 – 400 cm-1, diamonds described as predominantly etc. depending on the secondary hue, and 11,000 – 7,000 cm-1, 1 cm-1 resolution, tone, and saturation. These fancy colour up to 1024 scans, at room temperature). diamonds are also often well documented Raman and photoluminescence spectra due to their high price and rarity (Kane, were recorded using a Renishaw inVia 1987). However, precisely because of Raman microscope (488 nm, 514.5 nm, this rarity, studies have been few and and 632.8 nm laser sources, at liquid there is very little understanding of the nitrogen temperature). possible origins of the red and near-red colours in natural diamonds. Recently, we have had an opportunity to examine Results a fancy reddish brown diamond, which The natural diamond of 0.202 ct, cut is shown in Figure 1. Systematic non- as a round brilliant, contains mineral destructive spectroscopic investigations inclusions easily visible in dark-ﬁ eld under optimum measurement conditions illumination under a gemmological have been carried out to record its microscope. After careful observation optical absorption features and possibly and comparison, the colour was graded Figure 1: Fancy reddish brown diamond of 0.202 relate them to the origin of its colour. as fancy reddish brown according to the ct. Photo by H. Ito. UV-Visible-near infrared (UV-Vis-NIR) GIA system, which is very close to red.

A fancy reddish brown diamond with new optical absorption features

to transmission near 700 nm. At liquid spectra excited by an Ar-ion laser with nitrogen temperature, a weak but clear both 488 nm and 514.5 nm wavelengths absorption band at 776 nm was detected at liquid nitrogen temperature were (Figure 3b). Although a 776 nm band recorded. A strong and broad emission has been occasionally detected in band centred about 710 nm was detected. photoluminescence spectra in natural Sharp emission bands of 637 nm, 692 blue diamond with red phosphorescence nm, 704 nm, 818 nm and 905 nm are (Johnson and Moe, 2005), to the best of superimposed on both sides of this broad our knowledge, this is the first recorded band (Figure 5). Under the Ar-ion laser, observation of a band at this position in relatively strong red luminescence is the UV-visible absorption spectrum of a visible even with the naked eye. natural diamond. Details of the infrared absorption Discussion and summary Figure 2: The reddish brown diamond showed spectrum are shown in Figure 4 and Pink to red (or purple) diamonds green-yellow fluorescence when examined using suggest that the diamond is mostly type can be obtained from yellow to brown the UV fluorescence imaging system of the DTC Ib with minor IaA. The 1332, 1344, DiamondView. Growth features resembling script type Ib diamonds, whether natural or -1 are visible in the image. 1353, 1358, 1374 and 1387 cm peaks synthetic, when subjected to irradiation are all nitrogen related (Figure 4a, and and annealing treatment (Collins, 1982). The stone was inert under both long-wave see Zaitsev, 2001). However, two weak The colour is primarily due to a broad (365 nm) and short-wave (254 nm) UV absorption bands at 6169 cm-1 and absorption band centred at 550 nm, and lamps, but it displayed weak green-yellow 4702 cm-1 were detected in the 7000 – to the irradiation and annealing treatment- fluorescence when examined in the DTC 4000 cm-1 range (Figure 4b). The small related absorption bands, such as GR1 DiamondView imaging system (Figure 2). 4702 cm-1 band has been reported by (741 nm), N-V centres (575 nm, 637 nm), A growth pattern consisting of short Fritsch et al. (1991), without attribution to and the 595 nm band, which are usually dark lines disposed at approximate right its cause, but an extensive search of the detected using advanced spectroscopic angles and resembling script is visible literature has not yielded any mention techniques (Moses et al., 1993). Since in the image. This probably represents of the 6169 cm-1 band which is clearly these absorption features are absent from agglutination of numerous tiny octahedral present in this diamond. the spectrum of the near-red diamond, crystals in sub-parallel orientation at an The Raman spectrum of the reddish its colour is probably natural. The weak early stage of the diamond’s formation. brown diamond was recorded and 776 nm absorption band in the visible The UV-visible spectrum at room contains the standard diamond peaks range and a clear 6169 cm-1 band in the temperature is shown in Figure 3(a). with no exceptional features. To further infrared absorption spectrum are new It shows complete absorption below characterize the spectroscopic features of absorption features in this diamond, but 500 nm with a steep absorption curve this diamond, photoluminescence (PL) it must be stated that strongly coloured

a b

3 0.64

776 nm 0.63 absorption absorption 1 absorption 776 nm 776

0 0.62 300 400 500 600 700 800 785 770 775 780 785 Wavelength (nm) Wavelength (nm)

Figure 3: (a) Visible absorption spectrum of the reddish brown diamond at room temperature showing a steep absorption curve from 700 nm to complete absorption below about 500 nm. (b) A weak absorption band at 776 nm is present in the spectrum when the stone is cooled with liquid nitrogen.

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A fancy reddish brown diamond with new optical absorption features

natural diamonds often show previously a 1.9 undocumented spectroscopic features 1130 which may or may not turn out to have diagnostic value. 1.5

The infrared spectrum shows that the 1344 diamond is predominantly type Ib with 1387 1332 1332 1358 1358 absorption in the visible range caused 1 1353 1353 by single nitrogen atoms in the diamond absorption 1374 1374 structure. However this absorption may 0.5 be augmented by a band near 485 nm which occurs in diamonds showing 0.2 a broad photoluminescence peak 1400 1300 1200 1100 1000 -1 near 700 nm. Collins and Mohammed Wavenumber (cm ) (1982) ﬁrst drew attention to this band, although their diamonds exhibited yellow photoluminescence under long- b 0.05 wavelength UV whereas the reddish brown diamond was inert. 0.04 Although the cause of colour in this 4702 near-red diamond is not yet clear, the spectroscopic data could prove helpful 0.02 when combined with data from similar

stones in the future. absorption 6169 0 Acknowledgement The authors thank Dr Ichiro Sunagawa, emeritus professor of Tohoku University −0.02 and Yoshiko Doi, AGT Gem Laboratory 7000 6000 5000 4000 and GIA Japan for their valuable Wavenumber (cm-1) comments and support. Figure 4: (a) The infrared absorption spectrum shows that the diamond is a type Ib with minor IaA. (b) There is a clear 6169 cm-1 absorption band and a small peak at 4702 cm-1 in the 7000–4000 cm-1 References range. Collins, A.T., 1982. Colour centres in diamond. J. Gemmology, 18, 37-75 Collins, A.T. and Mohammed, K., 1982. Optical studies of vibronic bands in yellow luminescing natural diamonds. 692 J. Phys. C., 15, 147-58 50000 Fritsch E., 1998.The nature of colour in diamonds. In: G.E. Harlow (Ed.), 40000 637 (N-V)− The Nature of Diamonds, Cambridge University Press and American Museum 30000 of Natural History, New York, 1998, 818 counts 20000 23-47 Fritsch, E., Scarratt, K., and Collins, A.T., 905 10000 1991. Optical properties of diamonds 552.4 (diamond Raman) with an unusually high hydrogen 0 content. In: New Diamond Science and 600 700 800 900 1000 Technology – Proc. Second Int. Conf. Wavelength (nm) on the New Diamond Sci. and Tech., R. Messier, J.T. Glass, J.E. Butler and Figure 5: Photoluminescence spectrum of the reddish brown diamond showing a strong broad R. Roy (Eds), 1991, Mater. Res. Soc., emission band centred around 710 nm. The spectrum is the result of excitation by an Ar-ion laser Pittsburgh, PA, 671-6 (514.5 nm) at liquid nitrogen temperature.

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Johnson, P., and Moe, K.S., 2005. Strongly colored natural type IIb blue diamonds. Gems & Gemology, 40, 258-9 Kane, R.E., 1987. Three notable fancy- color diamonds: purplish red, purple- pink, and reddish purple. Gems & Gemology, 23, 90-5 King, J.M., Moses, T.M., Shigley, J.E., and Liu, Y., 1994. Color grading of colored diamonds in the GIA Gem Trade Laboratory. Gems & Gemology, 30, 220-42 King, J.M., and Shigley, J.E., 2003. An important exhibition of seven rare gem diamonds. Gems & Gemology, 39, 136-43 Moses, T.M., Reinitz, I., Fritsch, E., and Shigley, J.E., 1993. Two treated-color synthetic red diamonds seen in the trade. Gems & Gemology, 29, 182-90 Zaitsev, A.M., 2001. Optical Properties of Diamonds: A Data Handbook. Springer -Verlag, Berlin, p.502

The Authors

Taijin Lu, Tatsuya Odaki, Kazuyoshi Yasunaga and Hajime Uesugi AGT Gem Laboratory, Okachimachi CY Building, 5-15-14 Ueno, Taido-ku, Tokyo 110-0005, Japan Tel: +81 3 3834 6586; Fax: +81 3 3834 6589; email: [email protected]

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A place for CZ masters in diamond colour grading

Michael D. Cowing FGA

Abstract: Over the last 20 years and despite recommendations to the contrary, many gemmologists and appraisers have gravitated to the use of cubic zirconia (CZ) master stone sets to assist in the colour grading of diamonds. This investigation revisits with new insight, diamond grading technique and methodology. It addresses the judicious use of CZ master stone sets to augment diamond masters that are smaller in size and number. Study results support the use of accurately graded, carat-size CZs in reducing the subjectivity of colour grading when only incomplete (every other grade) diamond master sets of small (under 0.4 ct) sizes are available. Keywords: colour grading, cubic zirconia, CZ, diamond

Introduction 3. The pros and cons in the use of CZ acknowledged degree of subjectivity to This investigation explores historical master stones in diamond colour colour grading. guidance in the use of diamond master grading. It is helpful to examine how the stones, and offers a rationale for 4. A study of grading environments Gemological Institute of America (GIA) augmenting master stone sets of smaller involving a multiplicity of lighting has addressed and answered the need for and fewer diamonds with a full set of types resulting in additional accurate and consistent colour grading. carat size CZ masters. The question recommendations for colour grading In 1941 the GIA introduced “a method addressed is: Can the acknowledged using CZ or diamond master stones. of grading diamond colours against a subjectivity of diamond colour grading be 5. An evaluation of CZ master stone sets standard in the form of a definitely set reduced by supplementing an incomplete from two main manufacturers. and constant scale, as incorporated in set of smaller diamond master stones the new GIA Colorimeter. This is the with a complete set of larger CZ masters? GIA’s development of a first time a colour-grading ‘yardstick’ has Along with two gemmologist-appraiser colour grading system been established.” “Thus, the problem of colleagues, the author also conducted and Accurate colour grading of diamonds the relative colour of the grades seems reports on a study of the accuracy of eight has been and remains one of the difficult to have been largely solved for the ten-stone sets of CZ master stones, four challenges facing dealers, laboratories, jeweller who has a series of key stones from each of two main manufacturers of gemmologists and appraisers. As (GIA Masters) graded on the ‘yardstick’” these sets. diamond prices continue to rise, so (Shipley and Liddicoat, 1941). Figure 1 is a Findings are reported of studies in five does the necessity for accurate colour representation of that numerical ‘yardstick’ areas related to diamond colour grading: determination. Today, a single colour and its relation to the GIA letter grades 1. The historical development by the grade difference in, for example, a and to the master diamond grades. The Gemological Institute of America (GIA) 2 ct, VS1, round brilliant can mean over letter grades, which correspond to the of a colour grading standard beginning a 20% change in its value. A mistake in numerical grade ranges of the ‘yardstick’, with the GIA colour grading ‘yardstick’. grading can have this sort of large impact were introduced by GIA in 1953. The 2. Industry and GIA teaching of methods on appraised value. With amounts like D-Z letter grading system has become the and recommendations for colour this in the balance, it is incumbent upon ‘lingua franca’ of colour grading in the grading using GIA Diamond Masters, the graders of diamond colour to be as United States and largely worldwide, and which reduce the subjectivity of colour accurate as possible despite the myriad of GIA graded, master diamond sets have grading. confounding factors that add an industry- become the standard reference tool for

A place for CZ masters in diamond colour grading

objects. This can be accomplished by using enclosures like those of the GIA DiamondLite and DiamondDock (Figure 3) or, as is often done, by using white-plastic diffusers over the light source and enclosing the diamond in a folded white card. 2. Clean the diamond to be graded and, if needed, also clean the master stones. Especially in the whiter colour grades, any dirt, particularly on the girdle, is liable to lower the apparent colour, Figure 1: GIA ‘yardstick’, letter grades and GIA diamond master stone positions which define the possibly by as much as a grade or letter grades. more. 3. To prevent distracting reflections and diamond colour grading. The relationship carat, ideal cut, whole-grade master dispersion colours, use a dull, flat white between the letter grades, the numerical diamonds from E to L and N. Because of background such as the several plastic grades of the GIA ‘yardstick’, and the the expense of retaining diamonds of this trays from suppliers of gemmological position and range of each master grade is size or larger for each colour grade, most equipment, the GIA DiamondLite or shown in Figure 1. Notice the numerous small grading laboratories, gemmologist- Diamond Dock trays or accordion- brackets indicating the position and range appraisers and jewellers have purchased folded white paper or cardboard. of each grade relative to the GIA colour- only a small number of quarter to third A non-fluorescing background is grading ‘yardstick’. carat masters. Appraisers and laboratories prescribed, but observation of industry GIA master diamonds are graded with certified by the American Gem Society practice and personal experience twice the accuracy of standard grading, (AGS) and the Accredited Gemmologist indicates that either non-fluorescent so they in turn can be used for standard, Association (AGA) are required to have at material or common white paper whole-letter diamond grading. A master least five GIA-graded masters of a quarter containing a blue fluorescent dye work G, for example, is within a quarter grade carat or larger. equally well, as long as they are flat range around the F/G border (1.5 ± white with no bluish tint under the 0.125), compared to the standard grade of illumination used in grading. G, which has a full grade range between Prescription for accurate the F/G border and the G/H border (1.5 colour grading to 1.999). A review of the guidelines for the There is little to no argument with the use of GIA-graded diamond masters is view that a third carat or larger, complete important. These instructions help reduce set of GIA-graded master diamonds, like subjectivity caused by the many variables those shown in Figure 2, is the best tool that can affect colour grading. These for accurate colour grading. They are guidelines are from the organizations, second-generation diamond master stones literature and grading manuals of GIA having been graded against the primary and AGS and from the experience of master stone set, which is often referred to professional diamond graders. as the ‘master master’ colour grading set at 1. Grading should be done in a lighting GIA (G. Roskin, pers. comm.) environment of diffuse, daylight- In Figure 2 is a complete diamond equivalent illumination free of Figure 3: GIA Diamond Dock, photograph by master stone set of nine, heavy-third coloured reflections from adjacent Jonathan Weingarten

Figure 2: Complete set of GIA-graded diamond master stones from E through L and N.

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A place for CZ masters in diamond colour grading

from a fluorescent tube in the 5000 K to 5500 K range. Examples are the ‘full spectrum’, tubes such as the Ott Light. Excellent colour discrimination can also be made in the 4200 K colour temperature of a cool white fluorescent. The principle is that the illumination, like a diamond’s immediate surroundings, should be flat white without a blue or yellow tint. Additionally, all these fluorescent tubes and the ones in the GIA DiamondLite and DiamondDock emit a component of UV, which needs to be considered when grading diamonds that fluoresce from UV excitation, but that is a subject for another article. 5. Place the master stones table down with increasing colour left to right, as in Figure 5, in order to look into their pavilions in directions perpendicular to the pavilion facets or parallel to the girdle. Figure 4: Foreign buyers area, trading floor of the Israel Diamond Exchange, courtesy Israel On the basis of the tone/saturation of Diamond Exchange its colour, place the diamond being 4. The GIA’s prescription for the grading Notice that in spite of the available graded between the master stones illumination is daylight equivalent daylight from the large area of North closest to it. If it fits just above a G light. In past years, GIA recommended facing windows, and ceiling mounted master stone, for example, (which and used in their grading the daylight fluorescents, those examining the GIA graded to be within a quarter fluorescent tubes of their DiamondLite. diamonds are employing the lighting grade of the F/G boundary), the colour In addition to the DiamondLite, the from standard desk lamps. grade is F. If it fits just below the G GIA Diamond Course (GIA, 1994) True daylight varies widely, but the 4200 master, the colour grade is G. This stated: “Filtered, cool white, balanced K of a cool-white fluorescent to the 5500 procedure assumes a master stone for fluorescent light is best.” The term K colour temperature of noon daylight, every grade. Many sets are incomplete, ‘cool white’ is associated with northern and up to the 6500 K of blue skylight are and where there are missing colour daylight, as ‘warm white’ is with prescribed for diamond grading. Of this masters, visual interpolation of the incandescent light. Because warm white range of daylight colour temperatures, grade between the surrounding master is roughly every colour temperature the 6500 K daylight fluorescent tube is diamonds is necessary, or the more from 2000 K to 4000/4500 K, the range a little too bluish-white for some, the difficult extrapolation of the grade is of cool white is lighting above 4500 K author included, who find better colour necessary if the diamond is outside the to the 6500 K of the standard daylight discrimination under noon-daylight colour range of the masters. (D65) fluorescent tubes (pers. comm., R. Geurts). (Note that in fluorescent lighting cool colour temperatures begin at the 4100 K of the ‘cool white’ fluorescent.) Many gemmologists employ the small daylight fluorescent with white plastic diffuser attached to their GIA microscopes. Also in wide use by the trade is the eighteen-inch, daylight, 15-watt fluorescent tubes in a standard desk lamp. An example of their use can be seen in Figure 4 which shows

dealers on the trading ﬂoor of the Israel Figure 5: Six CZ masters and one diamond (colours E-K) in the tray of the Diamond Dock, diamond exchange. photograph by Jonathan Weingarten.

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A place for CZ masters in diamond colour grading

Figure 6: CZ master sets, colours E-L from manufacturer B (top row) and manufacturer A (bottom row).

6. To minimize confusion when for colour grading. Small laboratories, and Howard Rubin GG of Gem Dialogue comparing the unknown diamond's such as the author’s AGA Certified Gem Systems (pers. comm.) relate that they can colour to the masters, these reference Laboratory, and gemmologist- appraisers, much more effectively arrive at a colour diamonds should be of similar well- who have obtained AGS's Independent grade of a carat or greater size diamond made cut and proportions. They Certified Gemmologist Appraiser (ICGA) using carat size CZ masters than by using should be of Cape series, yellow hue, designation, are required to grade with at the smaller and fewer stones of their with no distracting inclusions, no least a five-diamond master set. However, diamond master sets. They and others more than faint fluorescence, and be many gemmologist-appraisers, the author find that a more accurate grade can be similar in size with a minimum 0.25 included, feel it is necessary to use a obtained with a 10 stone master set of ct weight. Master stones should not complete set comprising each of the most carat size CZs than can be obtained with a have thick and/or unpolished girdles, important whole letter grades from E to L small, incomplete set of diamond masters. as these features can cause confusion. or lower. Al Gilbertson (pers. comm.), one of the Unpolished girdles trap dirt and metal A sample of 38 gemmologist-appraisers two original AGS, ICGA appraisers with particles with handling, which can listing their colour grading equipment over thirty years experience, states that lower their perceived colour a grade or on the Internet revealed that 16 listed a when on appraisal assignment outside more. combination of diamond and CZ master the laboratory, he would take on the road This is the prescription for accurate stones, seven listed only CZ, and 15 listed with him a set of CZs that he had checked colour grading using diamond masters. only diamond. periodically for accuracy against his Attention to these instructions aids in This small sample indicates that many diamond master stone set. His diamond reducing the subjectivity in diamond gemmologist-appraisers have found a masters remained in his laboratory, while colour grading. place for CZ in master stone sets. Many he risked only the loss of the relatively jewellers and others in the industry have inexpensive CZ masters. He would For and against CZ master employed CZ masters since they became compare his CZ masters once or twice a stones for colour grading available over 23 years ago. The appeal of week against diamonds graded by GIA to With all the vigilance needed in the CZ Masters is an economic one. Because develop familiarity and skill in their use. use of diamond colour master stones, of the poor economy of tying up large Gilbertson’s point was not to shun the use what are the pros and cons in the use of amounts of money in larger diamonds, of CZs, but to be practised in their use CZs as masters? most master stone sets consist of quarter when the need arose. Periodic practice A sidebar from GIA's Diamond Grading to third carat sizes of four or more and checking of CZs raises proficiency in Course (GIA, 1994), titled “No CZ for diamonds. Without a master diamond their use and would reveal any possible D-Z” makes it clear that GIA writers and for each grade, visual interpolation or colour change. educators have advised against the use of extrapolation is required, which increases The laboratory of David Atlas GG, CZs as master stones for colour grading. the subjectivity of colour grading. In President of D. Atlas & Co. Inc. (pers. The reasons given are the different yellow addition, disparity in size makes precise comm.), employed several sets of CZ hue, confusing reflections from CZ’s comparison of colour more difficult, master stones in their colour grading and greater dispersion, the difference in lustre, and comparing the colour of a small GIA-graded diamond master stones were and the concern over CZ’s colour stability. quarter or third carat diamond master to used to check frequently for any colour Any case made for the use of CZ masters a carat or greater size diamond requires change in the CZs. has to address these concerns. considerable skill only obtained through Several diamond wholesale dealers Large laboratories such as those of practice and experience. known to the author use CZ master sets the GIA and the AGS have multiple sets Both James Naughter GG FGA of A&A in their buying. The often-narrow margins of GIA-graded diamond master stones Gemological Laboratory (pers. comm.) in their wholesale transactions mean that

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A place for CZ masters in diamond colour grading a one-grade mistake in colour grading yellow cape series diamonds to the yellow Using all five lighting environments, can make the difference between profit hue of CZ masters. the author found the same colour and loss. Their success in the practical Addressing the concern for the colour determination in each of these use of CZs in diamond buying and colour stability of CZ, the experience of the illuminations. This established that CZ’s grading is testimony to the accuracy, and author and of other owners and CZ-master different absorption spectrum and varying usefulness of their CZ masters. manufacturers is that the type of CZ amounts of fluorescence did not result in For many, CZs have become a material used by the two main suppliers, colour changes (metameric failure) large recognized and accepted tool in diamond one for over 22 years, has proved to be enough to cause additional error in colour colour grading. All these examples largely stable under normal care and use. grading. support the usefulness of CZ masters in The differing absorption spectra of Experimenting with these five different the colour grading of diamonds. diamonds and CZ raises concern for lighting environments resulted in the possible colour shifts (called metameric surprising finding that colour differences Considerations specific failure) in different illumination were more apparent and colour environments. A way to avoid this comparisons were more easily made in to the use of CZ in colour possibility is by grading (and periodic cool white and ‘full spectrum’ fluorescent grading checking and recalibrating against lighting (colour temperatures from 4200 For those who currently use or who diamond masters) under lighting similar K to 5500 K). Colour differences of a are contemplating using CZs for colour to illumination the manufacturer of the grade or less were more difficult to grading diamonds, there are a few factors CZ set recommends and uses in his initial see and evaluate in the slightly bluish- to consider in addition to the guidelines grading. Experiments by this investigator, white daylight fluorescent and the LED listed for GIA diamond master stones. grading in five different lighting lighting (colour temperatures 6500 K Of foremost importance is having a environments, yielded the same colour and above). This finding is interesting, CZ master stone set that is accurately grading determinations. This finding because, on one hand, it is at odds with graded against a full, reference GIA reduces the concern for possible colour the widespread prescription for north diamond master set. The CZs should shifts, as there was no apparent metameric daylight equivalent (6500 K) lighting correspond in tone and saturation and be failure. Relative to the diamond masters, (Bruton, 1978), while on the other hand, close in hue to their diamond master set no colour shifts of the CZs were observed. it supports GIA's Diamond Course (GIA, equivalents. The biggest problem is the 1994) statement: “Filtered, cool white, accuracy and evenness of colour spacing balanced fluorescent light is best.” The of these master sets. After all, the GIA Evaluation of CZ master author suggests trying both to find a master diamonds are a ‘second generation’ stone sets personal preference. having been graded against the ‘master To provide a preliminary assessment The B master sets contained the master master primary set’. The CZ master sets of currently available CZ master stone stones D through L and N, while the A are third generation stones incorporating sets, a number were obtained from sets contained the stones E through N. possible accumulated (or cancelled) errors several different vendors of gemmological The sets were evaluated as a 10 stone of two graders. equipment. All these suppliers carry CZ whole, and then re-scored for the more A revealing test of initial accuracy and sets from either or both of two sources, important eight grades E through L, evenness of spacing of a ten stone master designated A and B in this study. shown in Figure 6, which both sets have set of either diamond or CZ is to mix Purchased were eight, 10 stone sets, four in common. them up, and by eye try to put them back from each manufacturer. The purpose was The author graded all eight sets, in order of increasing colour. Assuming to evaluate the accuracy of the sets. and David Atlas and James Naughter normal colour vision, if your placing This investigator graded each set against graded four sets apiece, two from results in the set being out of order, it is a background of accordion-folded flat each manufacturer, and the results the set that is the problem. white paper with his complete diamond are given in Table I. It is important to In considering the hue differences master set. To check for any possible acknowledge that the errors measured between CZs used as masters and the colour shift in different lighting due to CZ’s are a combination of errors in the yellow tints in type 1a, Cape series different absorption spectrum and varying manufacturers’ gradings, differences diamonds, these are small and not small amounts of yellow fluorescence, the between our three master stone sets, and nearly as difficult as comparing the tone/ grading was done for each stone in five any errors in grading by the three of us. saturation of a pale grey or pale brown different lighting environments. These were The author had the advantage of a full diamond with the pale yellow, Cape a daylight fluorescent, a daylight fluorescent set of diamond master colour grades, series, master diamonds. The author and through a lexan plastic filter to remove UV, while James Naughter used a GIA and those interviewed for this article found a cool white fluorescent, a ‘full spectrum’ AGS graded five diamond master set, and little difficulty comparing the colour of fluorescent, and a white LED lamp. David Atlas used a full set of CZs graded

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A place for CZ masters in diamond colour grading

Table I: Results of grading by D. Atlas (DA), M. Cowing (MC) and J. Naughter (JN) of four A This ﬁrst error measure, which (A1-4) and four B (B1, 3, 5, 7) CZ master stone sets. determines how close the CZs were to their labelled grades, ﬁnds that the A sets Set Grader D E F G H I J K L M N have an average per stone error, over MC - Hi E E/F E F/G Hi I Hi J H/I I(

Table II: Closeness of CZs to their labelled grades; errors measured in units and decimal points of one grade.

Set A Set B 10 Worst Worst Worst Worst 8 error 10 error 8 error Set Grader error error error Set Grader error error ave. average average ave. in 10 in 8 in 10 in 8 MC 1.25 2.5 1.31 2.5 MC 0 0 0 0 A1 B1 DA 0.95 1.5 1 1 DA 0.1 1 0 0 MC 1.45 3 1.5 3 MC 0.1 1 0.13 1 A2 B3 JN1111 DA0.110.13 1 MC 1.5 3 1.5 3 MC 0.2 1 0.13 1 A3 B5 DA 0.85 2 0.75 2 JN 0.1 1 0.13 1 MC 1.05 2 1.13 2 MC 0.2 1 0.13 1 A4 B7 JN 0.8 1.5 0.75 1.5 JN 0.2 1. 0.25 1 MC 1.31 3 1.36 3 MC 0.13 1 0.09 1 A# B# DA & JN 0.9 2 0.88 2 DA & JN 0.13 1 0.13 1 N.B.: A# = average for all stones, or worst in all stones B# = average for all stones, or worst in all stones. DA denotes D. Atlas, MC denotes M. Cowing and JN denotes J. Naughter

Page 82 The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

A place for CZ masters in diamond colour grading

Table III: Closeness of CZs to their equivalent diamond master stones; errors measured in units and decimal points of one grade.

AB 10 Worst 8 Worst Worst Worst 10 error 8 error Set Grader error error error error Set Grader error error average average ave. in 10 ave. in 8 in 10 in 8 MC 1 2.5 1 2.5 MC 0.25 0.5 0.19 0.5 A1 B1 DA 0.65 2 0.5 0.5 DA 0.6 1.5 0.5 1 MC 1.05 2.5 1.13 2.5 MC 0.2 0.5 0.13 0.5 A2 B3 JN 1.2 1.5 1.25 1.5 DA 0.6 1 0.56 0.5 MC 1.28 2 1.23 2 MC 0.25 0.5 0.19 0.5 A3 B5 DA 0.95 2 0.75 2 JN 0.1 1 0.13 1 MC 1.18 2 1.29 2 MC 0.4 1.5 0.25 0.5 A4 B7 JN 0.71 1.5 0.7 1.2 JN 0.32 1.5 0.34 1.5 MC 1.13 2.5 1.16 2.5 MC 0.28 1.5 0.19 0.5 A# B# DA & JN 0.88 2 0.8 2 DA & JN 0.41 1.5 0.38 1.5 N.B.: Symbols as in Table II. whose dates of assembly are not known. when, as is frequently the case, the and assistance with organization and It may be, for example, that the A and B available diamond masters are relatively editing. sets were assembled at different times. small in number and/or size. The study The implications of this survey for sets findings and results also support the References in the future are not quantifiable by the argument that an accurate and complete Bruton, E., 1978. Diamonds. 2nd edn. author. set of CZ masters can, by themselves, be Chilton Book Co., Radnor, PA. 532 pp effectively employed in diamond colour Gemological Institute of America, 1994. Conclusions grading, if periodically checked for Diamonds – Diamond Grading, The main benefits of this study are in retention of that accuracy. Assignment 10 – Grading Color, 21 pp showing the practical use of accurately Shipley, R.M., and Liddicoat, R.T. Jr., 1941. graded CZ master stone sets, and the Acknowledgements A solution to diamond color grading factors and methodology in their proper Thanks to the following individuals problems. Gems & Gemology, 3(11), use, demonstrating the importance of for their contributions, discussions, and 162-8 verifying the initial accuracy of the set, suggestions: David Atlas, Al Gilbertson, and making periodic checks against full, Raymond Mason, James Naughter, Howard diamond master colour grading sets to Rubin and Peter Yantzer, and special ensure retention of that accuracy. thanks to Richard Cartier for suggestions Interested gemmologist-appraisers are encouraged to explore for themselves why CZ masters have found a place in The Author the colour grading of diamonds. This Michael Cowing FGA investigation finds that CZ masters have AGA Certified Gem Laboratory a contribution to make in reducing the email: [email protected] subjectivity of diamond colour grading

Page 83 Gem-A Workshops As the world’s longest established gem educator, The Gemmological Association of Great Britain is the leading provider of the most up-to-date and comprehensive knowledge regarding gemstones and retail staff training. With highly qualiﬁed tutors, fully-equipped classrooms and a wide variety of teaching stones for students to examine, we provide all of the essentials for top-quality training. Our workshops are held from 10:00 am to 4:30 pm each day (unless otherwise stated) at our headquarters near Hatton Garden, one of London’s ﬁnest jewellery quarters.

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The geological context of gems in the Velasco Pegmatitic District, Argentina

Fernando Guillermo Sardi

Abstract: The Velasco Pegmatitic District is located in the Velasco range, La Rioja province, northwestern Argentina. The Velasco range is made up of several granitic units of different petrography, magmatic evolution and age among which are the Huaco and Sanagasta granites. The pegmatites in the Velasco district have a spatial and genetic relationship with these granites and belong to the rare-element class, beryl type, beryl-columbite- phosphate subtype. The pegmatites are usually zoned and the K-feldspar zone is generally the most important for gem-quality beryl. Heliodor and aquamarine varieties are present and these crystals can be cut to yield products of attractive beauty. Other beryl crystals with poor transparency can be utilized for cabochons or tumble polished. Rock-crystal and rose- quartz are also present in some pegmatites from the Velasco district.

Keywords: aquamarine, gemstone, heliodor, pegmatite, rock crystal, rose quartz, Velasco range

Introduction 67°00′ 66°30′ The Velasco range is located in the central Alpasinche N region of La Rioja province, northwestern Argentina (Figure 1). It is the largest Aimogasta 28°30′ mountainous unit of the geological province of the Sierras Pampeanas, which is characterized by large volumes of

Velasco range crystalline rocks of several origins and ages. Beryl-bearing pegmatites are found in the Huaco Granite (Toselli et al., 2000) 29°00′ and in the Sanagasta Granite (Grosse and Sardi, 2005). For this reason, each BOLSON granite is considered a lithological guide Area of the DE HUACO to possible gem occurrences (Sardi, 2005). Velasco range Both granites have mainly porphyroid LA RIOJA CITY textures, without signs of deformation. 29°30′ Their outcrops occupy much of the central-north and central-east zones of the 0 10 20 30 km LA RIOJA Velasco batholith (Figure 2). The Huaco PROVINCE Granite covers 620 km2 and the Sanagasta Study area Granite 240 km2 (Grosse and Sardi, 2005), 200 km Velasco Pegmatitic District and the Huaco Granite contains more

Be-pegmatites than does the Sanagasta Figure 1: Location of the study area. On the right is the outline of the Velasco Range, and the Granite. indicated study area.

The geological context of gems in the Velasco Pegmatitic District, Argentina

67°10′ 67°00′ 66°50′ Pinchas N Aguas Blancas

29°00′ 29°00′

Kismiango

Las Peñas

29°10′ 29°10′ Huaco

Bolsón de Huaco

Sanagasta 0 5 10 km 29°20′ 29°20′

LA RIOJA CITY

67°10′ 67°00′ 66°50′

Key to symbols: Quaternary sediments Sanagasta Granite Undifferentiated granitoids Pegmatites Deformed granitoids Huaco Granite Metamorphic rocks (La Cebila Formation)

Figure 2: Simpliﬁed geological map of the Velasco Pegmatitic District. Modiﬁed from Sardi and Grosse (2005). Bolson de Huaco is an area which is a topographic depression covered with Quaternary sediments.

The pegmatites lie in the Velasco belonging to rare elements class; beryl Geological setting District of the Pampean Pegmatitic type and beryl-columbite-phosphate The Velasco range consists of a Province as defined by Galliski (1994). subtype (Galliski, 1994; Sardi and Grosse, mixture of Palaeozoic granitic rocks of Herrera (1968), in a local classification, 2005). different origins and evolutions. Such grouped the pegmatites from the Pampean The aim of this communication is to rocks of I-type affiliation in the south and Pegmatitic Province into four categories record some gem-quality minerals in the granitoids of S-type affiliation towards the following a course of fractionation from pegmatites. Most are beryl, and of lesser centre and north of the range can clearly ‘type 1’, barren pegmatites with oligoclase, importance is quartz. Beryl is an accessory be distinguished (Toselli et al., 2002, 2005; to ‘type 4’, highly evolved with Li mineral in the Velasco pegmatites and Bellos, 2005). In the south, the granitoids mineralization. In this case, the pegmatites has been extracted only sporadically and are granodioritic and tonalitic with from Velasco District correspond to the in an inconsistent manner during the last hornblende and magnetite as accessory ‘type 3’ which is characterized, in general, century. At the moment only gem-quality minerals, and per- and meta-aluminous by a simple zonal structure, by high stones are being recovered. Mineralogical tendencies in their compositions; while in diversity and abundance of accessory and gemmological studies of such the north, the rocks are shallow magmatic minerals, and by the appearance of a deposits in the area are very scarce, and porphyroid granites with two micas, phase of substitution of potassium by the data presented below are preliminary, and with a per-aluminous character. The sodium. Subsequently, they have been and represent a beginning for more plutons in the centre and north of the classified, according to Cerný (1991) as detailed research.

Page 86 The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

The geological context of gems in the Velasco Pegmatitic District, Argentina

Velasco range comprise the Aimogasta occasionally mantled by plagioclase bodies present more or less homogeneous Carboniferous Batholith (Toselli et al., generating a Rapakivi-like texture characteristics as to their structures and 2006) and they are intrusive into deformed (Grosse and Sardi, 2005; Grosse et al., mineral composition. According to Sardi et orthogneisses of Ordovician age and 2008). Another difference is that the al. (2002), their contacts with the granitic also commonly into protomylonites and Sanagasta Granite has a higher biotite/ host-rock are sharp. mylonites of Ordovician to Devonian age muscovite ratio than the Huaco Granite. The lengths of the pegmatites are no (Toselli et al., 2006). The matrix is essentially composed of greater than 250 m and most consist of a On the east flank of the Velasco range, quartz, microcline, plagioclase, biotite marginal-external zone, an intermediate the La Cebila Formation is represented and muscovite. The geochemical studies zone and core of quartz (Sardi, 2005). by sporadic outcrops of meta-pelites made by Grosse et al. (2008) indicate the The marginal-external zone wraps and meta-psammites. These sediments granites to be silica-rich, potassium-rich, around the coarse-grained minerals in the are of Upper Precambrian – Lower ferroan and alkali-calcic to slightly calc- pegmatite. It is aplitic and/or equigranular Cambrian age (Aceñolaza et al., 2000), alkalic. U-Pb monazite age determinations fine- to medium-grained leucogranite and their metamorphic grade does not on Huaco and Sanagasta Granites indicate and is composed of quartz, microcline, exceed greenschist facies. In the extreme Lower Carboniferous crystallization ages plagioclase, tourmaline, muscovite, north of the range, contact metamorphic and the isotopic and geochemical studies biotite, apatite, and topaz (Sardi, 2005). rocks appear whose mineral association indicate a mainly crustal source, possibly The intermediate zone contains mainly indicates nearby shallow-level granitic similar to the Ordovician peraluminous quartz with microcline and/or plagioclase, intrusions (Rossi et al., 1997). metagranitoids which are nearby (Grosse with microcline being the more common; The Huaco (Toselli et al., 2000) and et al., 2008). perthitic and graphic textures are also Sanagasta (Grosse and Sardi, 2005) common. The accessory minerals in this Granites make up the whole of the Velasco District pegmatites zone are muscovite, scarce biotite, apatite, Aimogasta Carboniferous batholith. The Velasco District has numerous triplite, beryl and tourmaline (Sardi, Petrographically, their main characteristic pegmatite bodies that are developed 2005). Herrera (1971) and Ricci (1971) is a porphyroid texture with megacrysts immediately north, east and south of had already reported garnet, fluorite, of perthitic microcline, in some places Bolsón de Huaco (see explanation in columbite-tantalite and wolframite which making up to 50 % of the rock (Sardi the caption of Figure 2). The area of the can be added to this list. The core of the et al., 2002). These megacrysts are Velasco Pegmatitic District is occupied pegmatite is massive quartz, usually grey white in the Huaco and pink in the by the Huaco and Sanagasta Granites but some is pink. Here, the accessory Sanagasta Granites. The Sanagasta and the Be-pegmatites have a spatial minerals are very scarce: tourmaline, granite's K-feldspar megacrysts are relation with them (Figure 2). These muscovite and beryl (Sardi, 2005).

a b c

d e f g

Figure 3: Beryl from the Velasco Pegmatitic District. Milky beryl: (a) Green and pale green beryl; the left and centre fragments show striated faces, and in the one on the left a hexagonal contour is visible. Width of image 12.2 cm. (b) Idiomorphic yellow beryl. Width of image 3.2 cm. (c) Pale blue (turquoise colour) beryl – aquamarine. Width of image 0.6 cm. Translucent and transparent beryl: (d and e) Heliodor varieties, associated with grey quartz. Width of images: 1.5 cm and 0.6 cm respectively); (f) Heliodor with feldspar and mica. Width of image: 1.7 cm. (g) Fragment of aquamarine. Width of image 1.8 cm.

Page 87 The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

The geological context of gems in the Velasco Pegmatitic District, Argentina

a b c d

Figure 4: Faceted examples of heliodor and aquamarine. (a and b) Heliodor, 7 mm long, on different backgrounds and under different lights; weight 0.615 ct. (c and d) Aquamarine, 5 mm square, on different backgrounds and under different lights. Weight 1.279 ct. Gemstones ﬁrst-order prisms and basal pinacoids, yellow variety of beryl, heliodor, has total Beryl although some crystals appear wedge- transparency, scarce fractures and is free shaped. The mineral size is variable. of inclusions of other minerals (Figures Beryl is generally concentrated in Transverse sections of the crystals measure 3d, e and f); pale green and pale blue the intermediate zones associated with up to 6 cm and the longest crystals are up aquamarine (Figure 3g) reach lengths of anhedral quartz, clusters of muscovite and to 12 cm. When the mineral is associated about 3 cm. The almost total absence of K-feldspar (Sardi, 2005). Most beryls are with muscovite, beryl is thin and long, fractures in heliodor and aquamarine can green, yellow and pale blue (Figures 3a, but in association with grey quartz it is permit their cutting and polishing to give b and c) but varieties of colourless beryl thicker. A poor cleavage can be present beautiful and attractive stones (Figures are very scarce and are associated mainly parallel to (0001). Only rarely does it 4a, b, c and d). Some gem-quality crystals with quartz. The beryls are idiomorphic, have inclusions of other minerals such as of beryl may be so embedded in quartz and have vitreous lustre and conchoidal tourmaline, quartz and muscovite. that it is difﬁcult to extract them without fracture. According to Sardi (2005), most The economic importance of beryl fracturing; these may be more desirable are well-developed hexagonal prisms, from the Velasco Pegmatitic District lies and valuable for mineral collectors some with vertically striated faces (Figure in its gem quality (Sardi, 2005). The as heliodor or aquamarine in matrix. 3a). The most common forms are Goshenite is very scarce and small in size relative to heliodor, and thus is less a c important. Non-gem-quality crystals of beryl are of greater size and range from translucent or semi-translucent to milky. They have only minor commercial value, and some may be cabochon cut or polished by tumbling. Gem-quality crystals are considered to have originated in the later stages of cooling and crystallization of the pegmatitic cavity and may be secondary b or recrystallized.

Quartz There is more than one generation of quartz in the pegmatites and the gem- quality quartz is considered to have been formed during the later pegmatitic (or hydrothermal) stage. The variety rock crystal has been found in the intermediate zone of the pegmatites in association with K-feldspar. It is colourless, entirely transparent, idiomorphic with hexagonal Figure 5: (a and b) Typical rock crystal, 42 contours and without inclusions. Crystals mm long, on different backgrounds and under different lights; weight 4.2252 g; (c) A specimen reach 4.2 cm in length and 1 cm in width of rose quartz, 96 mm high, with a rough top and (Figure 5a and b). Rose quartz has been polished sides.

Page 88 The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

The geological context of gems in the Velasco Pegmatitic District, Argentina found in pegmatites in the Sanagasta Bellos, L., 2005. Geología y petrología Velasco y Famatina. Provincia de Granite, generally forming part of the del sector austral de la sierra de La Rioja. Argentina. VIII Congreso core-quartz of the pegmatites (Figure 5c). Velasco, al sur de los 29º 44’ S, La Geológico Chileno, II, 1498-501 It is coarsely crystalline and in some is Rioja, Argentina. Serie de Correlación Sardi, F., Toselli, A., and Rossi, J. N., 2002. very transparent and free of inclusions. Geológica INSUGEO, 19, 261-78 Estudio geológico preliminar de las The quartz gems are secondary in Cerný, P., 1991. Rare-element granitic pegmatitas del Norte del Bolsón de importance to the beryl. pegmatites. Part I: Anatomy and Huaco, sierra de Velasco, La Rioja. XV Internal evolution of pegmatite Congreso Geológico Argentino, II, 33-4 Conclusions deposits. Geoscience Canada, 18(2), Sardi, F. G., 2005. Petrografía y At present, gem-quality beryl and 49-67 caracterización de la mena del quartz can be recovered from the Galliski, M., 1994. La Provincia Pegmatítica distrito pegmatítico Velasco, La Rioja, pegmatites of the Velasco District Pampeana. I: Tipología y distribución Argentina. XVI Congreso Geológico (Argentina). Most of the gem beryl occurs de sus distritos económicos. Argentino, V, 231-8 in idiomorphic prisms of yellow, green Asociación Geológica Argentina, Sardi, F. G., and Grosse, P., 2005. or pale blue, in sizes up to 12 cm in Revista, 49(1-2), 99-112 Consideraciones sobre la clasificación length, and with different degrees of Grosse, P., and Sardi, F., 2005. Geología del distrito Velasco de la Provincia transparency. Some crystals of heliodor de los granitos Huaco y Sanagasta, Pegmatítica Pampeana, Argentina. and aquamarine are large enough to have sector centro-oriental de la Sierra de XVI Congreso Geológico Argentino, V, commercial value. The formation of the Velasco, La Rioja. Serie de Correlación 239-42 gems is attributed to crystallization in the Geológica INSUGEO, 19, 221-38 Toselli, A., Rossi, J., Báez, M., Grosse, late stages of pegmatitic evolution. Future Grosse, P., Söllner, F., Báez, M., Toselli, P., and Sardi, F., 2006. El Batolito studies, especially of a thermometric A., Rossi, J., and De La Rosa, D., 2008. Carbonífero Aimogasta, Sierra de nature, could yield further insight into Lower Carboniferous post-orogenic Velasco, La Rioja, Argentina. Serie de their origin. Gem-quality quartz in these granites in central-eastern Sierra de Correlación Geológica INSUGEO, 21, pegmatites occurs as rock crystal and rose Velasco, Sierras Pampeanas, Argentina: 137-54 quartz. U-Pb monazite geochronology, Toselli, A., Rossi, J., Miller, H., Báez, geochemistry and Sr-Nd isotopes. M., Grosse, P., López, J., and Bellos, Acknowledgements International Journal of Earth Sciences L., 2005. Las rocas graníticas y The author thanks Dr Jorge Saadi (in press) metamórficas de la Sierra de Velasco. (Consulting Geological, Córdoba province, Herrera, A., 1968. Geochemical evolution Serie de Correlación Geológic Argentina) and Geol. Fernando Campos of Zoned Pegmatites of Argentina. INSUGEO, 19, 211-20 (Miguel Lillo Fundation, Tucumán Economic Geology, 63(1), 13-29 Toselli, A., Rossi, J., Sardi, F., López, J., province, Argentina) for advice on Herrera, A., 1971. Pegmatitas de la sierra and Báez, M., 2000. Caracterización gemmological aspects of this work. The de Velasco y de la sierra Brava, petrográfica y geoquímica field-work and laboratory studies were provincia de La Rioja; estructura, de granitoides de la sierra de carried out as part of the investigation mineralogía y genesis. I Simposio Velasco, La Rioja, Argentina. 17 projects of CIUNT (National University of Nacional de Geología Económica, I, Geowissenschaftliches Lateinamerika- Tucumán, Argentina) under the leadership 245-58 Kolloquium (LAK), CD-Proceedings, of Dra. Juana Rossi. The photographs Ricci, H. I., 1971. Geología y evaluación paper Nº 81, pp. 6. Institut für of the Figures 3, 4 and 5 were kindly preliminar de las pegmatitas de la Geologie und Paläontologie der provided by my friends Paul Grosse sierra de Velasco, Departamento Universitat Stuttgart. Germany and Miguel Báez (National University of Capital, Sanagasta y Castro Barros, La Toselli, A., Sial, A., and Rossi, J., 2002. Tucumán, Argentina). Rioja. Dirección Provincial de Minería Ordovician magmatism of the Sierras de La Rioja. pp. 50. Unpublished. Pampeanas, Sistema de Famatina and Rossi, J. N., Toselli, A., Durand, F., Saravia, Cordillera Oriental, NW of Argentina. References J., and Sardi, F., 1997. Significado Serie de Correlación Geológica Aceñolaza, F., Miller, H., and Toselli, A., geotectónico de corneanas piroxénicas INSUGEO, 16, 313-26 2000. Geología de la sierra de Velasco, en granitos de las Sierras de Paimán, provincia de La Rioja, Argentina. 17 Geowissenschaftliches Lateinamerika- The Author Kolloquium (LAK). CD-Proceedings, paper Nº 1, 6 pp. Institut für Geologie Fernando Guillermo Sardi und Paläontologie der Universitat INSUGEO-CONICET. Miguel Lillo 205, (4000) San Miguel de Tucumán, Argentina Stuttgart, Germany [email protected]

Page 89 Gem-A's new Open Distance Learning Gem-A (ODL) Courses in Scottish Branch Gemmology Conference 2009

Friday 1 May to Monday 4 May Launched in 2008, Gem-A's new Foundation in Gemmology ODL Course is ideal for students The Queen's Hotel, who need the fl exibility to work from home and the ability to plan their own schedule. You Perth, Scotland will learn about commercially important gem materials as well as a range of treated and imitation products. This popular annual event attracts speakers The course includes distance tuition, a student web login, online tuition and assessed course and participants from work, examinations and student registration. many corners of the world. It is essential that our students have internet The well-balanced programme of lectures access to complete the course. Students receive comprehensive and fully illustrated has something for anyone with course notes, a gem reference guide, a gem an interest in gems. testing kit and 20 study stones. UK ODL students receive three practical tutorials at Gem-A’s London headquarters. Overseas Speakers will include: students can either attend the UK tutorial sessions, or may arrange sessions with a KENNETH SCARRATT (KEYNOTE) Gem-A approved local provider. CLARE BLATHERWICK Foundation Certifi cate in Gemmology ALAN HODGKINSON The Foundation course is assessed by course work and a fi nal examination, with BRIAN JACKSON an emphasis throughout the course on the practical aspects of handling gem materials. JENNIFER SCARCE Those who qualify are awarded the Foundation DR HANCO ZWAAN Certifi cate in Gemmology and are eligible to continue their studies with Gem-A's Diploma in Gemmology course. Sunday afternoon will be devoted to displays, demonstrations and workshops, Next start dates: 12 January 2009 – intensive 6 month and a fi eld trip will be held on the Monday programme morning. 16 March 2009 – the 9 month programme

Course fees: £1695 for UK students (to include the London Social events are held each evening, practical workshop) including the Ceilidh (dinner/dance) £1395 for overseas students on the Saturday.

F Full details of the ODL and other courses For further information or to book provided by Gem-A are given at contact Catriona McInnes on www.gem-a.com/education.aspx 0131 667 2199 or call +44 (0)20 7404 3334 email [email protected] for information The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

Magnetic susceptibility, a better approach to deﬁning garnets

Dr D. B. Hoover FGA FGAA (Hon.), C. Williams FGA, B. Williams and C. Mitchell FGA

Abstract: Using a new, non-destructive method of gem testing, magnetic susceptibility, the authors show how the major end- member composition of any garnet may be conﬁdently predicted by plotting RI against measured susceptibility. On this diagram, eight end-member garnets are plotted, so that any measured garnet can be placed in an appropriate ternary area. This method shows how previous methods of identifying garnets — by their colour, RI and spectrum — are insufﬁcient to accurately identify chemistry in the garnet group. Furthermore, it can be done with inexpensive equipment available to most gemmologists.

Keywords: garnet, gem testing, magnetic susceptibility, refractive index, speciﬁc gravity, UV-Visible spectra

Introduction only conventional gemmological testing we will consider eight of them, adding Most gemmologists classify garnets based equipment. Few non-destructive tests knorringite and goldmanite to the more on their colour, refractive index (RI) can give a better idea of the chemistry. familiar six (Table I). The mineralogist and absorption spectrum1,2,3,4,5,6,7. As new When the RI is plotted against magnetic names any of the mixed garnets by the sources and new gem varieties of garnet susceptibility, a more complete picture of name of the dominant end-member12. are discovered, and as our information on a garnet’s chemistry can be made. While Thus, although a pyrope may contain less garnet chemistry increases, problems with this new characterization technique raises than 50% of the pyrope molecule, it can the present gemmological classification questions about the current nomenclature still be the dominant component when become more apparent8. The practising and classification of gem garnets, we more than two end-members are present, gemmologist needs a better means for will stick to the chemistry and leave which is commonly the case. characterization of garnets to avoid such nomenclature and classification to future Due to the difficulty of getting problems. In this article, the authors will debate. sufficient compositional information show how any gemmologist can closely Most modern gemmological texts quickly and easily, gemmology infer the major end-members composition identify six garnet end-member species; has generally followed a different of a garnet — without expensive or high- the pyralspite group — pyrope, almandine nomenclature, opting to define nine tech equipment. and spessartine; and the ugrandite group varieties of garnets: pyrope, pyrope- Two of the authors introduced a — grossular, andradite and uvarovite8,10,11. almandine, almandine, almandine- new method of gem testing — magnetic A garnet species in its theoretical pure spessartine, spessartine, spessartine- susceptibility — in a recent paper9. Due form is referred to as an end-member, pyrope, grossular, grossular-andradite, 5,6,7 to the presence of transition metals in however they have not been found pure and andradite . Uvarovite is normally many garnets, the garnet group provides in nature. Natural garnets are always a not included as it has limited gem an interesting range of stones to which mix of several end-members, typically significance. To date, gemmologists have this method can be applied. Our research with three to five species of significant not come to an agreement on what value further confirmed that far more accurate quantity12. The mineralogist recognizes of RI should mark the separation between garnet composition can be revealed in this fifteen garnet end-members — some of way than was previously possible with which exist only in theory12. In this article Spessartite garnet. Photo by R. Weldon.

Magnetic susceptibility, a better approach to defining garnets

Table I: Properties and chemical formulae of the end-member garnets considered in this paper. how treating two physical properties as independent variables, one can Volume susceptibility End-member RI SG (calc.) Chemistry plot the compositions, and yet another (k) (calc.) × 10-4 SI physical property on the same graph. Pyrope 1.714 3.582 -0.225 Mg Al Si O 3 2 3 12 In essence, one can put the information

Almandine 1.829 4.315 40.7 Fe3Al2Si3O12 of the eight plots of Sriramadas, on one 14 Spessartine 1.799 4.197 47.45--- Mn3Al2Si3O12 graph. Winchell uses RI and cell length

Grossular 1.734 3.594 -0.225 Ca3Al2Si3O12 on the Y and X axes, and shows SG variation within each ternary diagram, Andradite 1.887 3.859 30.76 Ca3Fe2Si3O12 which now becomes a general triangle. Uvarovite 1.865 3.850 12.9 Ca3Cr2Si3O12 He recognizes, as others have, that SG Goldmanite 1.834 3.765 6.9 Ca V Si O 3 2 3 12 is not a very reliable measurement for Knorringite 1.875 3.835 13.68 Mg Cr Si O 3 2 3 12 determining chemical composition. N.B. 12, 18 The Manson and Stockton papers1,2,3,4,5 note that virtually all gem garnets can be these arbitrary boundaries in the garnet identification methods must be non- described by five end-members; namely, chemistry continuum8. Adding further destructive. In a series of articles on the pyrope, almandine, spessartine, grossular, 12 to the confusion, gemmologists classify, garnets, Manson and Stockton 1,2,4 and and andradite. Deer et al. note that these mostly by colour, eight commonly-used Stockton and Manson3,5 presented an in- five members usually make up more than trade names of these nine varieties; depth study on 202 transparent, gem-quality 99% of any garnet’s composition. This will chrome pyrope, rhodolite, malaia, garnets that is invaluable to gemmologists be important in what follows. Stockton 5 +3 +3 colour-change pyrope-spessartine, for presentation of the chemistry and and Manson also note that Cr , V and +3 +4 tsavorite, hessonite, topazolite, Mali and physical properties of each of the studied Ti , , although important for colour in demantoid5. Note that these are their garnets. In their final paper of the series5 some garnets, can be treated as trace gemmological classes, not mineralogical (p.215), they set the precedent for the elements, and not as components of other classes. With trade names, it becomes yet garnet classifications currently in use. end-member gem garnets, at least for this more complicated, but no more accurate. Manson and Stockton obtained their method of classification. 6 From our studies, we do not believe accurate garnet chemistry analyses using Johnson et al. add another important that gemmologists, relying only on RI, microprobe equipment not available contribution to gem garnet chemistry with spectrum, and colour can reliably — or to the average gemmologist. It should a paper on the Mali grossular-andradite consistently — allocate the correct species be noted that while they measured the garnets. These gems are ugrandites with or varietal name to a garnet being studied. specific gravity (SG) of each gem, they typical yellow-green stones averaging Gemmological texts often imply, for do not use SG at all in characterizing about 80% grossular, 18% andradite and example, that tsavorite, because it is gem garnets5. In fact, they state (p. 216): 2% pyrope. It is important to note that coloured by vanadium and/or chromium, “Although we generally discourage the these are typically strongly zoned; hence, is allochromatic, when in fact it is a use of this property in gemmology, it their physical properties will vary as well combination of garnet end-members that nevertheless can provide some useful as their colour across the zonation. In creates the colour. Very often there is a indications.” We will see why they may these Mali garnets, pyrope is typically 2 third (or even more) end-member present, have done this later on. to 3% with almandine and spessartine that while less than 10% in quantity, can Mineralogists often use another method much less. They noted that mineralogists yet affect the RI and colour in such a of quantitative measurement of garnet, may use physical properties such as unit way as to lead to a false conclusion by — its unit cell length. This measurement cell length, RI and SG to determine garnet the traditional methods. Problems with of the length of one edge of the unit cell, composition from end-member values, and the current state of affairs will become from X-ray diffraction data, is not practical tested how well their data served to match apparent later in this paper. for the gemmologist. Sriramadas13 has determined chemistry. They found that, for published eight ternary diagrams for the the Mali garnets, RI correlated well with the History garnet group showing RIs and unit cell garnet chemistry, while there was poorer The mineralogical literature abounds lengths on the triangles. Winchell14 notes correlation with other physical properties, with papers on the garnets12. Much of that ternary diagrams are mostly used especially SG which was determined the information has limited relevance to estimate composition from measured hydrostatically. It would be expected that to gemmology in the classification and physical properties, but that generally since the Mali garnets are almost entirely identification of gem garnets, as stones of there are too few properties to uniquely grossular-andradite, only one property is gem quality comprise only a very small define the composition. Using the needed to define the chemistry and RI proportion of the whole, and gemmological garnet group as an example, he shows would do this.

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Magnetic susceptibility, a better approach to defining garnets

Adamo et al.7 recently described Table II: Some paramagnetic ions, their valencies, effective magnetic moments, and the correlations between physical properties square of the moment, which is proportional to the magnetic attraction. and chemistry for 17 gem-quality garnets Magnetic moment Magnetic moment squared in both the ugrandite and pyralspite Ion (experimental) (relative attraction) groups, and also examined IR spectral Transition elements: features to see what they may contribute 3+ 2+ to classification of the garnets. They Fe , Mn 5.9 34.8 concluded that IR spectra, in particular, Fe2+ 5.4 29.2 permit discrimination between the Mn3+, Cr2+ 4.9 24.0 pyralspite and ugrandite series. Their Co2+ 4.8 23.0 data generally agree with what was Cr3+, V2+ 3.8 14.4 found by Manson and Stockton1,2,3,4,5. Ni2+ 3.2 10.2 Three hessonites contained from 84.5 to V3+ 2.8 7.84 92.75% grossular with andradite the other 2+ major component at 5 to 14%. Pyralspite Cu 1.9 3.61 members were under 2.1%. The two Ti3+, V4+ 1.8 3.24 tsavorites measured showed about 90% Rare-earth elements: grossular, and 4% goldmanite (vanadium Dysprosium Dy3+ 10.6 112. garnet). Of ten pyralspites measured, Holmium Ho3+ 10.4 108. grossular contents ranged from 0 to 6.15%, Erbium Er3+, terbium Tb3+ 9.5 90. the andradite component was generally Gadolinium Gd3+ 8.0 64. under 1% but in one sample was 8.3%. Thulium Tm3+ 7.3 53. Uvarovite reached 1.7% in a chrome- 3+ pyrope, and goldmanite 3.65% in a colour- Ytterbium Yb 4.5 20. change pyrope-spessartine. The chromium Neodymium Nd3+, 3.5 12.2 content of a garnet may be expressed as praseodymium Pr3+ either uvarovite or knorringite, but since Europium Eu3+ 3.4 11.6 knorringite is stable only at very high Cerium Ce3+ 2.4 5.7 12 pressures (greater than 70-100kbar) , the Samarium Sm3+ 1.5 2.2 chrome in most gem garnets is probably better considered as part of the uvarovite previously thought but the two series do We will be primarily concerned with end member. An important exception may show structural differences and most gem magnetic susceptibility per unit volume, be in some gem chrome pyrope. garnets appear to fall within or close to k, a bulk property of all materials, that Adamo et al.7 used the same garnet one series or the other. can be directly measured. These materials nomenclature as Stockton and Manson5 can be classified in three distinct groups but added the variety grossular-andradite, Magnetic measurements according to the sign and value of their based on the work of Johnson et al.6 Modern understanding of magnetism magnetic susceptibility. It was in 1933 that Winchell shows that it arises from the motion of The orbiting electrons about an atom divided the garnet group into two electrons in atoms in the same way that of any material, when in the presence of series composed each of three major an electrical current in a wire produces an applied field, will precess, presenting a garnet species — the ugrandite series a magnetic field about the wire. Within weak opposing magnetic field. Precession (uvarovite, grossular, andradite), and the the atom, electrons move in orbits about is the wobble that a toy top makes pyralspite series (pyrope, almandine, the nucleus and also spin. Both of these when the spin axis is not in line with the spessartine). These two mineralogical motions produce very small magnetic vertical direction. If no other magnetic series do not appear to be as well known dipole fields, so the electrons act as very effects are present, these materials will to gemmologists as they should be. small permanent magnets within the atom. be weakly repelled by a magnet, and k Although complete solid solution between The magnetic property of any material will be negative. Such materials are called natural members of each series was is the resultant of the contributions of diamagnetic. Most gems are diamagnetic. believed possible, there appeared to be a all of its atoms and how this reacts to In some atoms and molecules there compositional gap between them. Modern an applied magnetic field. More on this is a net magnetization generally related studies on the garnets have shown complex subject can be obtained from to electron spin, but which in bulk is there to be more miscibility between Kittel15, college physics texts, or the zero due to thermal motion of the atoms. the various garnet end-members than Internet. However, when a field is applied they

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Magnetic susceptibility, a better approach to defining garnets can become oriented to give a small net positive susceptibility, overcoming the negative value due to diamagnetism. Such materials are called paramagnetic. The elements contributing to this type of magnetism, that are relevant to gemmology, are the transition and rare- earth elements. These elements, while best known for their colour causing properties, whether as major or trace components in many gems, also have paramagnetic properties. As shown in Table II, the manganese- and iron-bearing gems will have the greatest paramagnetic susceptibilities, as the rare-earth content of most gems is small. Thus, magnetic testing will indicate the presence or quantity of these elements, just as absorption spectra show their presence by the absorption of light. Paramagnetic gems are of the most interest in gem characterization and identification by means of susceptibility measurements. The table shows the square of the measured effective ion moment, because this is directly proportional to susceptibility. Ferromagnetic materials have much larger absolute susceptibilities than diamagnetic or paramagnetic materials due to a natural alignment of magnetic Figure 1: Apparatus used to measure magnetic susceptibility in this study. moments of the individual atoms. They are further distinguished by being made is generally difficult, mineralogists and previous article9, where the magnetic up of small individual magnetic domains gemmologists often marginalize the use of attraction (pull) between a very small in which the magnetization may not SG for characterization of their materials. Neodymium-iron-boron (NdFeB – or be the same as a neighbour. To the This is clearly one of the reasons that NIB) magnet and the flat table of a cut gemmologist, ferromagnetic minerals, Stockton and Manson5 didn’t make use of gem was measured on an electronic such as magnetite, are of interest where SG in their work. scale. If the NIB magnet pole face is they may be present as inclusions, but By having a new, independent, smaller in diameter than the gem’s table, are generally of less importance than quantitative physical property by which to then the pull is a direct measure of paramagnetic minerals. characterize gems, the gemmologist now the gem’s susceptibility. We have used In the past, non-laboratory has much greater scope to characterize cylindrical magnets of ¼, 3/16, 1/8 and 1/16 gemmologists have had only two truly gemstones than before. Not only can we inch diameters by ½ inch long. These N42 quantitative, physical tests available by measure a gem’s susceptibility, but we grade NIB magnets are available from which to characterize gemstones. These can also calculate what its susceptibility K&J Magnetics Inc. (www.kjmagnetics. are refractive index (RI and related should be from its chemistry when known; com). These are inexpensive, but very birefringence) and SG. Unfortunately, RI or, with certain assumptions, calculate the strong. We recommend following the and SG are not very independent variables, quantity of a transition metal in a gemstone manufacturers warnings regarding use. as many years ago Gladstone and Dale as shown by Hoover and Williams9. For the best precision, the largest magnet (quoted in Larsen and Berman16) showed that fits within the stone’s table should be that the ratio of RI to SG is approximately Making magnetic susceptibility used. For all measurements shown in this a constant, (RI-1)/SG=k. Because of the measurements paper we used a 1/8 inch magnet, which Gladstone-Dale relationship, and the The basic theory behind susceptibility allowed measurements on stones of one fact that accurate measurement of SG measurements has been described in a carat or larger. In order to convert this pull

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Magnetic susceptibility, a better approach to defining garnets

e Figure 2 (above): An early prototype using a photo stand. While less precise than later set-ups, this arrangement proved useful for g experimenting with the technique. f into a measure of the gem’s susceptibility one need only measure a material of known and consistent susceptibility — a standard. A standard can be any paramagnetic material in which the paramagnetic element that causes Figure 3 (right): Close-up of magnet and stone interface on scale. a) cylindrical NIB magnet; b) the magnetic susceptibility is equally stone under test; c) Blu Tack ring support to hold the stone; d) non-magnetic stone support; e) scale measuring cup; f) bridge support – to avoid pressure on the scale while the stone table is made distributed and in consistent quantity. parallel to the magnet face; g) scale’s active surface (underneath the bridge). For our testing purposes, we used cobalt are continuing to investigate ways to non-magnetic pedestal, table up, and held chloride (CoCl .6H O) with a pull of 0.855 2 2 improve the apparatus and technique, but in place with Blu Tack, then placed within ct (measured with one of our 1/8 inch (3.12 believe that their present method is quite the scale’s measuring cup. A number mm) magnets) and susceptibility of 9.87 × adequate for garnet characterization. of precautions need to be observed in 10−4 SI units. The equation below shows The current apparatus is a surplus order to obtain accurate and reproducible the relationship to determine an unknown biological microscope stand containing measurements. First, the magnet and gem susceptibility from pull measurements. a ﬁne focus mechanism, and an x-y table must be absolutely clean and free Equation 1 translation stage for centring the gem of all grease, dirt and dust. An antistatic k = C × Pull table with the magnet face. In place brush will help prevent static electricity where Pull = measured pull of the test of the microscope optics is a plastic from affecting measurements, as well stone and ﬁtting with a steel bolt at its centre, to as aid in the removal of charged dust, k (of standard) C = which a cylindrical magnet of whatever especially in cold climates. One needs to Pull (of standard) size needed may be placed. This holds regularly check the magnet pole surface,

the magnet in a fixed, stable, and rigid as these very strong magnets tend to As an example, a 3.10 ct pyralspite has position. The fine focus knob raises acquire minute specks of magnetic a pull of 1.135 ct with the 1/8 inch magnet. and lowers the microscope stage by particles, which must be removed before Its susceptibility, k =[9.87×10−4SI /.855 ct] micrometres, with a macro knob for larger measuring. ×1.135 ct = 11.54×10−4 SI/ct × 1.135 ct = adjustments. Once these precautions are satisfied, it 13.10×10−4SI. For measuring the force of the is critical to make the magnet pole surface The concept is very simple, but the magnetic attraction, a small digital scale and the gem’s table exactly parallel. This measurement must be done with care was placed on the microscope stage. We is done by placing the gem within a bit of and it takes some practice to become used a GemOro PCT50 scale, but any Blu Tack so that it is held in place along consistent. The equipment is shown similar scale that measures to 0.005 ct the girdle. A rigid bridge consisting of a 1/8 in Figures 1, 2 and 3. The authors should work. The gem is placed on a inch plastic sheet measuring 1 by 2 inches

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Magnetic susceptibility, a better approach to defining garnets

1.89 and. 0.5 3.85 1.88 knor. 1.87 uva.

1.86 UGRANDITE 3.8 1.85

1.84 gold. al. 1.83 4.3 3.75 1.82 0.5 4.2 1.81 0.5 0.5 1.80 3.7 sp. 1.79 refractive index refractive 4.1 1.78 0.5

1.77 4.0 3.65 M 1.76 3.9 0.5 1.75 PYRALSPITE

3.8 1.74

gro. 1.73 3.7 10% composition marks SG 1.72 ● malaia garnet py. 1.71 0 5 10 15 20 25 30 35 40 45 50 volume susceptibility x10−4 Figure 4: Plot of RI versus magnetic susceptibility for the garnet end-members pyrope, almandine, spessartine, grossular, andradite, uvarovite, goldmanite and knorringite. The pyralspite and ugrandite ternary triangles are shown with 10% triangles (red) shown along sides, and SG variations (blue) within each ternary. The purple data point (M) in the middle of the pyralspite ternary is that of a malaia garnet we measured. is placed above the scale’s recessed active at about 90 degrees difference, to be sure the scale is turned on and tared. Then the surface and the measuring cup placed on that they are parallel. Once the surfaces are microscope stage is gradually brought up this bridge. This then permits the magnet parallel, the microscope stage is lowered, to meet the magnet, and the maximum and gem table to be brought in contact the bridge removed, and the measuring attraction measured. A magnetic attraction and pressure put on the interface, so as to cup placed back on the scale. Again, check will show as a negative reading. Upon push the gem into the Blu Tack and align that the table and magnet face are parallel. contact of the magnet with the gem, the the two surfaces exactly parallel. With the In practice, we have had little problem in scale reading will go in a positive direction. bridge in place, the magnet is separated a parallelism after the bridge is removed if The maximum negative reading is the millimetre or less from the gem table, and care is taken. Next, the magnet and gem ‘pull’. This number is then converted to k, the surfaces viewed from two directions, are separated by several centimetres, and using the formula (1).

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A diamagnetic gem will give a very 4.40 small positive measurement, due to the 4.36 ‘push’ or repulsion of the stone by the al. magnet. For a 1/8-inch magnet, this will 4.32 typically be about 0.02 ct. 4.28 As more individuals try their hand at PYRALSPITE such measurements there undoubtedly 4.24 will be better methods developed for their 4.20 implementation. At present, this method sp. gives the best results for us. 4.16 4.12 RI = 1.8 Results A ternary diagram, sometimes called 4.08 a triangular plot, is a simple graphical 4.04 tool to show chemical compositions in a three-component system. The diagram 4.00 is an equilateral triangle where 100% of 3.96 a component is plotted at each triangle point. Zero percent of that component 3.92 RI = 1.76 would be at the opposite side and 3.88 the centre point of the triangle would specific gravity uva. and. represent 33.3% of each. They are often 3.84 knor. used to determine garnet composition, 3.80 and have been described and used in gold. the papers by Manson and Stockton1,2,3,4,5. 3.76 The pyralspite and ugrandite groups 3.72 UGRANDITE are examples, but if other garnet end- RI = 1.8 members are important in a garnet, 3.68 additional diagrams are needed. For 3.64 the ﬁve principal garnet end-members, gro. grossular, andradite, pyrope, almandine 3.60 py. and spessartine, ten ternary diagrams 3.56 would be required to cover all possibilities for three major components14. Where four 3.52 3.50 components are involved it becomes a bit 0 5 10 15 20 25 30 35 40 45 50 more complex, but details can be found in Volume susceptibility x10−4 SI 17 Hutchison (p.374 et seq.). Figure 5: Plot of SG versus magnetic susceptibility for the garnet end-members pyrope, almandine, Because many physical properties spessartine, grossular, andradite, uvarovite, goldmanite and knorringite. The pyralspite and ugrandite of minerals have been shown to be ternary triangles are shown with reddish purple lines indicating lines of constant RI. approximately linear functions of the Because we wish to distinguish dimension of a garnet, we will substitute proportions of their components, the between the various garnets, the the value of magnetic susceptibility ternary diagrams can also show the statement by Deer et al.12 (p.497) on the for this, and plot RI against magnetic variation of a physical property (P) subject is worth reviewing: “Within the susceptibility. This provides information with chemistry within the triangle14,17, garnet group the various species are best on the FeO and MnO that Winchell14 summarized in the following equation: distinguished by their RIs, SGs and cell called for. Equation 2 edges in conjunction, if possible, with partial chemical data, e.g. for FeO or P=Σ pimi =p1m1+p2m2+p3m3 ... MnO. The entry of even small amounts of Proposed new garnet the uvarovite molecule to the ugrandite where pi = the property of the ith end- characterization technique series imparts an emerald-green colour in In order to effectively use the plot in member such as RI, and mi = the mole percent of that end-member in the hand specimen; chrome-pyrope is usually Figures 4 and 5, one needs to understand composition. reddish but some show a green hue.” how the values of each end-member Because most gemmologists are not garnet are shown. The gemmological normally able to measure the cell edge properties of RI and SG, for the eight

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1.89 and. one prints the illustration to a piece of paper so that lines can be drawn and 1.88 knor. measured. Additionally, this is available for downloading from one of the author’s 1.87 uva. websites (www.stonegrouplabs.com go to 1.86 'Articles and Papers', then 'Garnet Chart'). UGRANDITE The scale of the printout is irrelevant. 1.85 From each apex of the pyralspite ternary, draw lines through the data point (the 1.84 gold. purple dot). Next, measure the length of al. 1.83 the line between the pyrope apex to the opposite base, and the length between 1.82 this base and the data point. When we did this, the measurements were 163 mm 1.81 and 77.5 mm. The ratio 77.5/163 = 47.5 is the proportion of pyrope in the garnet. 1.80 sp. Doing this for the other components, we 1.79 find 42% spessartine, and 11% almandine. These total 100.5% when added, showing refractive index refractive 1.78 minor graphical measurement error, but still a far more accurate idea of the 1.77 components than would otherwise be known. This malaia garnet would be 1.76 PYRALSPITE described as approximately Py47Sp42Al11. 1.75 The precision of all measurements is important to accurately define 1.74 the chemistry. Based on our repeat gro. measurements we estimate that RI should 1.73 be within +/- .001 and susceptibility about –4 1.72 +/- 1 × 10 SI. Thus, the error bars are of similar magnitude on the graphs for the py. 1.71 scales used, suggesting that each property 0 5 10 15 20 25 30 35 40 45 50 measurement contributes to a similar error Volume susceptibility x10−4 in chemistry. Figure 6: Plot of RI versus magnetic susceptibility for the garnet end-member data of Adamo et al.7 Note that it only requires values of Red crosses are calculated for all end-members found, blue crosses are for the three main end- RI and k to be able to specify the three members of each series. pyralspite components. A value of the end-member garnets we will consider, mark 10% intervals, with the 50% position SG, if accurate, would be able to confirm are taken from the mineralogical labelled (0.5). Blue lines and numbers the composition, or if accurate and not in literature12,18. The values for their magnetic mark SG values, assuming only pyralspite agreement would indicate the presence of susceptibilities have been calculated based or ugrandite components are present. one or more additional end-members. on ‘ideal chemistry’ as shown in Table I As can be seen in Figure 4, if one With this understanding, it should be and mean measured moments from Table has a pyralspite garnet with no other clear that if we take the malaia garnet II by use of the Langevin equation15. garnet components, then it must plot and add a little andradite, but keep the Figure 4 illustrates the basic plot within the pyralspite triangle, but if a pyralspite components balanced, the data used, with RI on the Y-axis and magnetic measured garnet is within the triangle, point would move up in RI, with very susceptibility (k) on the X-axis. Of the how does one determine what its little change in susceptibility. Adding a eight principal garnet end-members pyralspite composition is? Consider a little grossular would pull the point down plotted, the commonest six are joined to malaia garnet that we measured with an and to the left. In this figure, for clarity demonstrate the ternary diagrams. These RI of 1.762, and susceptibility of 24.1 × we have shown only the two principal are the pyralspite and ugrandite triangles 10-4SI. This is plotted in Figure 4 as a garnet ternary diagrams, but clearly (which are no longer equilateral) with the purple spot (M). From its position in the one could draw in all the others. Other end-member abbreviations shown at each triangle, it is apparent that this garnet is results presented below from pyropes corner. Small red triangles along each side a pyrope-spessartine-almandine. First, and almandines plot within the grossular-

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Magnetic susceptibility, a better approach to defining garnets pyrope-almandine triangle, indicating Table III: Comparison of measured and calculated properties of selected garnets from that these garnets most likely contain a Adamo et al., 2007. measurable grossular component. These can be computed in a similar Calculated on basis of Specimen Three manner to pyralspites or ugrandites, by Property Measured All end Composition — number main end closing the lines for the relevant triangle members grossular, pyrope and almandine. members

We want to emphasize that the only 1 RI 1.741 1.748 1.732 Py75Al14Sp0.7An8.3Uv1.7 change that we are making to long- SG 3.68 3.719 3.704 14 used mineralogical techniques is the Susc. # 8.79 6.69 substitution of magnetic susceptibility for 2 RI >1.79 1.812 1.81 Py Al Sp An unit cell length. 15 81 1.1 2.3 SG 4.19 4.190 4.196 Another way to present the RI, SG, and Susc. # 34.20 34.27 k data is shown in Figure 5, which has SG on the Y-axis and magnetic susceptibility 7 RI >1.79 1.803 1.803 Py.04Al12Sp87Gr0.4An0.6 on the X-axis, giving additional insights SG 4.13 4.207 4.212 into property variations. Figure 5 shows Susc. # 46.34 46.62 that there is an overlap between the 10 RI 1.775 1.769 1.767 Py34Al1.1Sp54Gr5.4Uv1.0Go3.6 pyralspite and ugrandite groups below an SG 4.00 3.935 3.963 SG of 3.86. The violet lines in each group Susc. # 26.53 29.11 mark lines of constant RI. The diagram 11 RI 1.738 1.742 1.741 Uv Gr An Py Sp clearly shows there is complete separation .05 93 5.1 1.4 0.7 between the two groups for indices above SG 3.59 3.612 3.607 1.80. This is particularly important for Susc. # 1.70 1.35 the identiﬁcation of garnets whose RI is 12 RI 1.741 1.740 1.737 Uv1.1Gr91An.05Py2.1Sp1.5Go3.7 above 1.80, where most gemmologists S.G 3.62 3.612 3.600 cannot obtain measurements. Thus, SG Susc. 0.94 0.45 can be substituted for RI using this new 16 RI >1.79 1.886 1.886 An Py Al Sp technique. As Figure 5 shows, andradite, 99.2 0.7 0.06 0.04 SG 3.88 3.857 3.857 almandine and spessartine can be distinguished on the SG-susceptibility Susc. 30.55 30.56 chart at the higher RIs. 17 RI 1.766 1.763 1.760 Uv0.1Gr78An19Py2.8Sp0.2 Using Figure 4 as the basic diagram S.G 3.66 3.645 3.680 and by taking published compositions Susc. 5.76 5.68 from the literature, we can now calculate NB: Calculation based on equation (2) what their RIs, magnetic susceptibilities Magnetic susceptibility all × 10-4 SI and SGs should be. This can be done using as many end-member components as we have values for. However, in using technique for indirect determination the pyralspite or ugrandite subgroups, such chemical data, one needs to be of garnet chemistry, permitting better and normalized to 100%, much as Manson aware of the problems of calculating end- characterization of the garnet group, is a and Stockton5 have done. The numbers member molecules from chemical analyses major step forward in gemmology. on each data point correspond to those as noted by Deer et al.12 Conversely, we of Adamo et al.7 The end-member garnets can estimate what the compositions could Determination of properties from (Table I) are indicated by green crosses be, based on the measured values of the chemistry and labelled. The pairs of red and blue properties, for each three-component As an example of using compositions crosses, generally, are fairly close. In system if we have two properties, or to determine properties, we have plotted Table III is a selection comparing these for four-component systems if we have on Figure 6 RI and susceptibility data calculated values against measured values values of RI, susceptibility and SG. In calculated for the pyrope and ugrandite given by Adamo et al. The analyses of many cases, there will be more than one garnets of Adamo et al.7 using equation the ten pyralspites showed seven end- combination of end-members that can ﬁt a (2). Values in red are derived using all members present, but no individual given physical property set. It is up to the the end-member compositions given by specimen with all seven. Four to six gemmologist to choose which possibility Adamo et al., while those in blue are for end-members were found between is most probable. We believe this new only the three main components of either these pyralspites, with half needing only

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Magnetic susceptibility, a better approach to defining garnets

1.90 The distribution of points in Figure 6 shows that for these gem garnets, 1.89 and. measurements of the RI and susceptibility correlate with the chemical composition 1.88 knor. rather well, remembering that the 1.87 red crosses represent the practical uva. measurements. Chrome pyrope, the 1.86 UGRANDITE garnet with the widest spread between red and blue values (specimen 1), shows 1.85 that it can’t be well characterized as a pure pyralspite and that some additional 1.84 component needs to be considered, such gold. 1.83 al. as andradite or uvarovite. The data of Adamo et al., although 1.82 far fewer in number, illustrate what Manson and Stockton1,2,4, and Stockton 4 1 1.81 and Manson3,5 found: in general, gem andradite and grossular fall close to their 1.80 10 respective end-members in the ugrandite sp. 1.79 ternary diagram; gem almandine and pyrope fall along the pyrope-almandine refractive index refractive 1.78 line with little spessartine present; and similarly for the almandine-spessartine 1.77 group. The malaia (specimen 9) and 2 7 PYRALSPITE colour-change (specimen 10) pyralspite 1.76 5 garnets are mainly spessartine-pyrope 1.75 with minor almandine. These values, we believe, are well correlated, including 1.74 3 those for SG. gro. 1.73 Estimation of chemistry from properties 1.72 For gemmologists, the most practical 1.71 py. and quick means of determining the 0 5 10 15 20 25 30 35 40 45 50 composition of a garnet is through Volume susceptibility x10−4 magnetic susceptibility. We have measured Figure 7: Plot of RI versus magnetic susceptibility for a series of garnets measured by the authors. The the RI and susceptibility of 39 gem pyralspite and ugrandite ternary triangles are shown. garnets from worldwide sources and the results are given in Table IV and Figure 7. four end-members to describe them. 6.1%, and 10% non-pyralspite components Grossulars plot close to the end-member, Grossular and andradite were the largest respectively. as do the andradites. In the pyralspite non-pyralspite components found. The In the ugrandite group specimens group, most almandine-pyropes show chrome pyrope, specimen 1 of Adamo’s (Table III and Figure 6), the data show little evidence of a spessartine component, list (Figure 6), shows the greatest the grossular garnets stretched out on and the almandine-spessartines show divergence between values based on the the grossular-andradite join up to about little pyrope. It is only the malaia garnets pyralspite component (blue cross within 20% andradite (specimen 17). This is a that have a strong mix of all three end- the pyralspite ternary diagram) versus similar pattern to that found by Manson members. In Figure 7 the RIs of stones complete chemistry. This stone had 8.3% and Stockton2. Some of the red crosses below 1.79 were measured with a andradite, and 1.7% uvarovite mixed do not show because of overlap with the conventional, critical angle refractometer. with pyrope, almandine and spessartine blue ones. In Table III the measured and Those with RI over 1.79 were measured components. The shift in graph position is calculated property values of a selection with a deviation angle refractometer, built toward the uvarovite-andradite positions, of the ugrandites can be compared. One by one of the authors (D.H.), making as would be expected. The other andradite (16) is essentially pure and this use of a laser pointer light source. The specimens in this series, 2–10, had 2.3%, is typical, as most natural andradites are accuracy of this device is estimated at +/- 1.6%, 4.01%, 5.04%, 1.25%, 0.98%, 0.8%, compositionally close to the end-member12.

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Magnetic susceptibility, a better approach to defining garnets

Absorption spectra and chemistry

A thorough investigation of the use a of absorption spectra to determine intensity (counts) 4000 garnet species would require another paper; so to indicate the diagnostic limitations of this method, only a few 3000 features of the pyralspite series will be discussed. In the pyralspite garnets, 2+ 2+ 2+ it is the Mg , Mn and Fe contents 2000 that determine the species. This

gives us three choices when looking transmittance at a pyralspite spectrum, if, for the 1000 moment, trace elements are neglected, there is either an Fe2+ spectrum, a Mn2+ spectrum, or both. Stockton and 0 400 420 440 460 480 500 520 540 560 580 600 620 640 5 Manson rely on the presence of the Wavelength (nm) 410 and 430 nm Mn lines to indicate if

any Mn is present. Rossman19 (p.218) b notes: “Only the sharp 410 nm band is intensity (counts) seen in the spectrum of many minerals 4000 with minor amounts of Mn2+ in the presence of greater quantities of Fe2+.” This raises the question of whether Mn 3000 lines in many garnets can be identified with the hand spectroscope, as these 2000 weak lines are commonly hidden in the obscurity of the blue end of the transmittance spectrum. Pearson20 also discusses 1000 the poor sensitivity at each end of the visible spectrum of the human eye and its limitations for identification of 0 absorption lines in the blue to violet 400 420 440 460 480 500 520 540 560 580 600 620 640 when using a hand spectroscope. Wavelength (nm) Figures 8a and 8b show pairs of Figures 8a and b: Graphs of transmission spectra for the four pictured garnets, showing similar spectra from garnets we have similarities between pyrope and spessartine spectra. a) Red line is a 2.24 ct spessartine (no. 1); measured (specimens 1, 2 and 3, 4) black line is a 4.19 ct pyrope (no. 2); b) Red line is a 1.61 ct oval spessartine (no. 4); black line is a in Figure 7. These transmission 4.73 ct pyrope (no. 3). spectra were run on an Ocean Optics and the 526 line could be seen by only hand spectroscope. With the hand S2000 Spectrophotometer. The classic one of the authors. No characteristic spectroscope, the authors observed only almandine absorption lines at about 505, manganese lines could be seen. iron lines at 510 and 575, with a cut-off 526 and 576 nm are present in all. In Figure 8b there are some small at approximately 430 for the 1.61 ct In Figure 8a the spectra of specimens differences in spectra of specimens 3 oval (red curve). The 526 line seen in 1 (spessartine) and 2 (pyrope) appear (pyrope) and 4 (spessartine), especially a 8b could not be distinguished with the nearly identical. In the region between shift in the two troughs (absorptions) near hand spectroscope. For the 4.74 ct pear 400 and 500 nm, note that the 410 575 nm between the two spectra. The shape, two authors observed a cut-off at and 430 nm absorption lines used by almandine lines are clearly prominent. 400 and 430 nm, strong lines at 575 nm, gemmologists to identify Mn2+ (5) are The cut-off in the blue is near 430 nm, a good line at 505 nm, and a weak line not present. This was confirmed with with no evidence of manganese lines at 526 nm. In each of these sets, one the hand spectroscope, where only at either 410 or 430 nm. There is also a stone is near the almandine-spessartine a cut-off at approximately 440 nm weak absorption near 460 nm, but this boundary with little pyrope, and the was observed. The 575 line was most is not recognized as a strong Mn line. other primarily pyrope (Figure 7). Yet apparent, the 505 was relatively strong, There are no Mn lines visible with the all stones have very similar colours.

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Magnetic susceptibility, a better approach to defining garnets

Table IV: Magnetic susceptibility and other properties of the garnets measured in this and ugrandite series’ ternary triangles are study. quite separate and do not overlap12,14. Clearly, a stone lying in the pyralspite Species or Weight No. Locality Colour RI k × 10−4 ternary area will have a limited amount of variety ct. any ugrandite component that could be 1 spessartine 2.24 ? deep red 1.810 43.8 present in order to fit measured physical 5 pyrope 3.42 Mozambique? red 1.751 12.5 properties. 7 malaia 2.78 E. Africa orange 1.762 24.1 The measurements of 39 stones plotted 10 almandine 2.57 India deep red 1.798 25.8 in Figure 7 reveal variations in gem 14 tsavorite 2.54 E. Africa medium bright 1.731 0.69 garnet chemistry that were not obvious green from previous gemmological work5,6,7,10. 15 demantoid 1.25 Russia green 1.892 25.5 Looking at the pyrope to almandines near the line (join) between the pyrope 24 hessonite 3.73 Sri Lanka? orange 1.741 2.54 and almandine end-members, it is clear 25 ‘uvarovite’ 17.97 Cab, S. Africa fine deep 1.795 8.53 that most of these have some measurable green component from the ugrandite series 28 rhodolite 1.55 Tocantins, purple 1.77 17.2 garnets. This is evident by their plotting Brazil at higher RI values than the line along 29 rhodolite 7.75 unknown purple-red 1.773 19.3 the join. If one looks at garnet chemistry given for example in Deer et al.12 for 0.004 and because the laser wavelength is was purchased as an Indian almandine, pyrope, chrome-pyrope, and almandine, 680 nm, the RI values were corrected for but it falls above the almandine-grossular most analyses show a significant ugrandite dispersion. join, so must have some andradite or component (or knorringite, in some From the data given in Figure 7, it chrome garnet component. A clue to its stones) with one of these being the is apparent that these garnets can easily probable composition is provided by second largest component. This had been be separated into pyralspite or ugrandite Deer et al.12 in the composition of one reported by Rouse10, but not emphasized. groups based on RI and susceptibility Indian garnet from Madras, which is Our data show that this is rather values. If there is any question, SG should Al61.4Py30.8An5.9Sp1.4Gr0.5. This composition common in gem garnets, and needs to be assist, due to the large density gradient gives a calculated RI of 1.796 and considered when discussing variations in between the two groups (Figures 4 and susceptibility of 27.4 × 10−4, remarkably garnet properties. 5). Of greater importance is the power close to that of the measured Indian Further research and testing of this this gives us in identifying the chemistry almandine (1.798, 25.8). If one calculates new method is called for in order to of a particular gem within the pyralspite the composition from its position in the confirm results from this method with or ugrandite groups. As an example, pyrope-almandine andradite ternary measured chemistry on more stones. The look at the garnet labelled 5 in Figure 7. diagram, one obtains a composition of current method is good for identifying the

This 3.42 ct stone is on the almandine- Al62Py30An8. This, we believe, is a good chemistry in terms of three end-members. pyrope line, so can be specified as example of what can be done with this To combine SG measurements with approximately Py68Al32 with an RI of 1.751 new technique. the current information will increase its and susceptibility of 12.5 × 10−4SI. Of complexity, but could more accurately course, a mix of other different garnet Discussion define the chemistry in terms of four end-members could be devised to give By plotting pairs of RI and end-members. For example, grossular and the same physical properties, but this susceptibility values for garnets as spessartine components in a stone can is the simplest. This stone was sold as shown in Figure 4 and following, one balance each other out, hiding evidence a Mozambique spessartine many years can directly define a garnet’s chemistry of both, as has been observed in some ago, but our data indicate clearly that it based on the composition of any three rhodolites. is predominantly pyrope. In colour, it is selected end-member molecules. Because The authors have presented a means close to the other three adjacent pyropes. it has been found that 99% of most for quantitatively measuring the magnetic The malaia garnet labelled 7 is an garnet compositions can be described susceptibility of cut gemstones as an example where three end-members are by a combination of the five common aid in characterizing their end-member present (see also M in Figure 4). It is garnet end-members5,12, the probable chemistry. In fact, any rough material approximately Py47Sp42Al11, compared compositions of any tested garnet are need only have one polished surface to the malaia measured by Adamo et quite restricted. to enable testing by this method. The al.7 (no. 9 in Figure 6), which was Additionally, by plotting RI and simplicity of the method makes it ideal for

Py52.7Sp33.6Al7.5Gr6.1. The garnet labelled 10 magnetic susceptibility, the pyralspite ﬁeld-testing new ﬁnds of garnet.

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Magnetic susceptibility, a better approach to defining garnets

It is recognized that trade and varietal 3. Stockton, C.M., and Manson, D.V., 12. Deer, W.A., Howie, R.A., and names of garnet will continue to be used 1982. Gem garnets: the orange to Zussman, J., 1982. Rock-Forming for commercial purposes. However, for red-orange color range. International Minerals. V.1A 2nd edn, Orthosilicates. gemmological purposes, we believe it Gemological Symposium Proceedings, Longman, London, 919 pp would be better to describe the actual Gemological Institute of America, 13. Sriramadas, A., 1957. Diagrams for end-member chemistry of a garnet derived Santa Monica, CA the correlation of unit cell edges and using this new method. The technique 4. Manson, D.V., and Stockton, C.M., refractive indices with the chemical overcomes the present RI and SG 1984. Pyrope-spessartine garnets with composition of garnets. American limitations as garnet identification methods. unusual color behaviour. Gems & Mineralogist, 42(3/4), 294-8 Further, it will allow new varieties to be Gemology, 20(4), 200-7 14. Winchell, H., 1958. The composition easily defined in the garnet continuum with 5. Stockton, C.M., and Manson, D.V., and physical properties of garnet. less confusion about their composition. 1985. A proposed new classification American Mineralogist, 42(5/6), for gem-quality garnets. Gems & 595-600 Acknowledgements Gemology, 21(4), 205-18 15. Kittel, C., 1956. Introduction to solid The authors would like to thank 6. Johnson, M.L., Boehm, E., Krupp, H., state physics. 2nd edn. J. Wiley, New colleagues in the trade, too numerous Zang, J.W., and Kammerling, R.C., York, 617 pp to name, for frank discussions of garnet 1995. Gem-quality grossular-andradite: 16. Larsen, E.S., and Berman, H., 1934. characterization, identification and a new garnet from Mali. Gems & The microscopic determination of the nomenclature. Particular thanks go to Gemology, 31(3), 52-67 non-opaque minerals. U.S. Geological Sylvia Gumpesberger for her persistence 7. Adamo, I., Pavese, A., Prosperi, Survey Bulletin 848, 2nd edn, 266 p in pushing us to examine, in a quantitative L., Diella, V., and Ajò, D., 2007. 17. Hutchison, C.S., 1974. Laboratory sense, what magnetic measurements might Gem-quality garnets: correlations handbook of petrographic techniques. do to advance the science of gemmology. between gemmological properties, J. Wiley & Sons, New York, 527 pp We wish to thank Grant Pearson for chemical composition and infrared 18. Meagher, E.P., 1982. Silicate garnets. in-depth discussion of eye-visible gem spectroscopy. Journal of Gemmology, In: Ribbe, P.H. (Ed.), Reviews in spectra. We are also indebted to the late 30(5/6), 307-19 Mineralogy, 5, Orthosilicates, 2nd Professor N. Haralyi whose early magnetic 8. Rouse, J.D., 1986. Garnet. edn., 25-66. Min. Soc. America, work first caught our attention, and Butterworths & Co., London, 134 pp Washington DC finally, our appreciation to an anonymous 9. Hoover, D.B., and Williams, B., 19. Rossman, G.R., 1988. Optical reviewer whose suggestions considerably 2007. Magnetic susceptibility for spectroscopy. In: Hawthorne, F.C. improved the paper. gemstone discrimination. Australian (Ed.), Reviews in Mineralogy, 18, Gemmologist, 23(4), 146-59 Spectroscopic methods in mineralogy References 10. Rouse, J.D., 1994. The Garnets. In: and geology, 207-54. Min. Soc. 1. Manson, D.V., and Stockton, C.M., Webster, R., revised by Read, P.G., America, Washington DC 1981. Gem garnets in the red-to-violet Gems, their sources, descriptions and 20. Pearson, G., 2003. Spectra of gem color range. Gems & Gemology, 17(4), identification, 5th edn. Butterworth- materials. Australian Gemmologist, 191-204 Heineman, Oxford, 191-206 21(12), 478-85 2. Manson, D.V., and Stockton, C.M., 11. Arem, J., 1987, Color encyclopedia of 1982. Gem-quality grossular garnets. gemstones. 2nd edn. Van Nostrand, Gems & Gemology, 18(4), 204-13 New York, 248 pp

The Authors D. B. Hoover Stone Group Labs, Springﬁeld, Missouri, USA. e-mail [email protected] C. Williams Bear Essentials, Jefferson City, Missouri, USA. email [email protected] B. Williams Bear Essentials and Stone Group labs, Jefferson City, Missouri, USA. email [email protected] C. Mitchell Gem-A, London. email [email protected]

Page 103 2009 EUROPEAN GEMMOLOGICAL SYMPOSIUM Organized by the Swiss Gemmological Society SGG/SSG Friday 5 June to Sunday 7 June 2009 Berne, Switzerland

The Swiss Gemmological Society is proud to invite all interested gemmologists to the 2009 European Gemmological Symposium.

Programme: Speakers will present a range of topics on diamonds, coloured stones, pearls and the jewellery trade, highlighting both the history of gemmology and state-of-the-art gemmological research. Keynote Speakers: Sir Gabi Tolkowsky and Martin Rapaport Further speakers include: Maggie Campbell Pedersen, Laurent Cartier, Jean-Pierre Chalain, Dr Eric Erel, Thomas Hainschwang, Vera Hammer, Prof. Dr Henry A. Hänni, Michael Hügi, Dr Michael S. Krzemnicki, Helen Molesworth, Andy Müller, Dr Daniel Nyfeler, Dr Jack Ogden, Vincent Pardieu and Roland Schlüssel Poster session: Details given at www.gemmologie.ch or email [email protected]. Contributions welcome.

Additional events (participation optional): • Welcome cocktail on the evening of Thursday 4 June and Symposium Dinner on Friday 5 June. • A visit of the mineral collection of the Natural History Museum in Berne during the afternoon of Friday 5 June. • An excursion to the famous crystal cave at Grimsel in the Swiss Alps on Sunday 7 June.

To book: For details on the pricing, registration and how to book a hotel in Berne, please visit www.gemmologie.ch.

Gem-A Conference 2009

Saturday 17 and Sunday 18 October The Hilton London Kensington Pencil it in ... The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

The refraction of light by garnet depends on both composition and structure

David K. Teertstra

Abstract: The index of refraction (n), used to identify minerals, depends on both composition and crystal structure. The method of optical analysis implies that a photon refracts by local interaction with individual ions. The index n is calculated exactly using a dependence of the speciﬁc refractivity of ions on the inter-ionic distances and angles of the crystal, and is inﬂuenced by bonds to surrounding ions up to half-a-unit-cell distant.

Keywords: crystal chemistry, crystal structure, garnet, index of refraction, optics, photon

Introduction refraction depends upon the composition both composition and crystal structure is This paper deals with controversial and structure. Each measured index of entirely absent. aspects of light and its refraction in refraction relates to a specific structure A general theory, relating each gems and minerals, and proposes a and state of cation order (Teertstra 2005, compositional and structural state (as model to deal with them. In this model, 2006). For a given structure-type (garnet expressed by the structural formula of for convenience, the particles have is considered here, see Table I), a change the mineral, e.g. Mg3Al2Si3O12 for pyrope) been called photons but it should be of composition directly relates to a to the specific physical properties, has understood that these particles have change in the optics, whereas for a fixed remained elusive. To make progress, some postulated properties that differ composition, polymorphs of minerals can one must understand both light and from those of the conventional photon of be distinguished optically (e.g. kyanite, crystallography. Historically, for example, quantum theory. The photon is a probe sillimanite, andalusite). That said, the the evidence for X-rays as a high-energy of the crystal structure. The energy of the relation between optical properties form of light rather than a new type photon is constant; the photon remains and composition has been precise only of particle was simultaneous with the intact and the wavelength is not reduced. for pure binary or ternary series, as a evidence for the structure of minerals The ions of each element have a specific theory relating optical properties to as ordered three-dimensional arrays of electric structure and a characteristic Table I: Physical properties (n, a, D) of end-member silicate garnets. contribution to the net index of refraction of the material. Accounting for the crystal Species formula n a (nm) Dcalc. structure, this new method of optical Pyr – pyrope Mg3Al2Si3O12 1.714 1.1459 3.5591 analysis also gives an accurate measure of Alm – almandine Fe Al Si O 1.830 1.1526 4.3184 composition. 3 2 3 12 Sps – spessartine Mn Al Si O 1.800 1.1621 4.1902 What a gem looks like depends on its 3 2 3 12 Grs – grossular Ca Al Si O 1.734 1.1851 3.5952 interaction with light, determined mainly 3 2 3 12 by the processes of reflection, refraction +3 And – andradite Ca3Fe 2Si3O12 1.889 1.2058 3.8507 and absorption. The optical properties of Uvr – uvarovite Ca3Cr2Si3O12 1.865 1.1996 3.8514 gems are essential to their identification. Gld – goldmanite Ca V Si O 1.834 1.2070 3.7651 Measurements of refraction can be 3 2 3 12 NB: n is refractive index; a is the unit cell edge; D is the density calculated from the diagnostic, mainly because the index of unit cell.

The refraction of light by garnet depends on both composition and structure atoms. From the equations of Bragg Mandarino 2007 for calculation of n from while magnetic flux occurs perpendicular and Laue, and by using the scattering oxides). to the electric plane. As light can be factors of ions, both the structure The equation for ions in crystals is described as an electromagnetic wave Σ and composition of a crystal can be n/D = (kidi), where ki is the molar ionic (Iksander, 1992), it must be acted on by determined. In thin-sheet diffraction, refractivity and di is the fractional density the electric force to effect refraction, but light is reflected only at specific angles (the weight of a number of ions i of this idea seems to be absent from physics. if the wavelength of light is similar to atomic weight AW per unit-cell volume For wave refraction, it is required that the distance between planar layers of V is also the ion weight fraction). For a the wavelength of light is reduced on atoms. However, the same information single ion, the refractivity is si = kiAW/An, entering a denser medium (e.g. yellow can be determined using the refraction in nm3, where An is Avogadro’s number. light in air is effectively blue in water), but data of a group of minerals, but using the The index of refraction is then a sum of such a reduction of wavelength is non- refractivity factors of ions. the partial contributions of the refraction observable and physically indeterminate. Σ Σ Although the photoelectric effect of each ion, with n = lnil = AN (si’ldil/ For a reduced wavelength, the quantum (now a subset of the theory of atomic AW). This modified Gladstone-Dale equation for energy (E = hc/λ where h is absorption, in which an atomic-electric equation (Gladstone and Dale, 1864; Planck's constant, c is the speed of light transition from a low-energy orbital to Teertstra, 2005) is offensive to wave and λ is wavelength) predicts an increased a high-energy orbital accompanies the theorists who insist that light does not energy, but this is also indeterminate. absorption of a photon by an individual interact with individual atoms, but the fact The wave theory assumes that light may atom) indicated to Einstein that light is a remains that the wave theory is complex be redirected (reflected or refracted) at local particle of similar size to an electron, and difficult to use and produces distinctly no energetic cost, so explanations for the only model of light currently available inaccurate values of n (e.g. Rocquefelte et thermodynamics or for the motion of results from the plane-wave solution to al., 2004, 2006). And although the theory free ions toward a light source (e.g. ion the Maxwell equations for electricity and of light as an electromagnetic wave has trapping by lasers) are absent. There are magnetism. The model of light as an had over a century of development, not also no fundamental explanations for electromagnetic wave requires the energy a single worker in physics has been able diffraction or for atomic absorption or to be spread out along the wavelength to relate the optical properties of crystals emission by single atoms. The current as well as across the wavefront, in to the structure using the theory. Also a situation in physics is that separate sets conflict with the physical evidence for a modified theory of light may be required, of equations exist for waves and for finite local particle of light. In the theory as a working model of the photon does particles, and the wave-like and particle- presented here, for example, each ion has not currently exist. like aspects of light are considered a specific refractivity and the net index complementary. The overall consensus of refraction is explained only if light From the wave theory of is that one cannot use light to gather consists of photons that interact locally light to a proposed local information about objects that are smaller with each ion. than the wavelength of light, but a glance The wave theory of light requires photon at the results in Table II indicates radii of Early workers in optics such as Isaac a homogeneous (or average) index refraction that are similar to atomic radii. Newton and Albert Einstein considered of refraction for materials, but the The main problem tackled here is that the interactions of light with matter mineralogical data indicate that the that the wave theory of light has only were best explained if light consists of a index of refraction (n) increases as the poor relations to the refractive properties stream of local particles. However, as the density (D) increases, so n α D, or n = of materials. Although it was known to interference patterns of light and of water KD. Such changes of n and D are due Maxwell that each pure material (e.g. waves appear similar, and as phenomena to substitutional exchange mechanisms diamond, sulphur) has a specific index of such as refraction are described by such as Mg <–> Fe that are common refraction (commonly determined using trigonometric functions, the earliest to many minerals. By considering that yellow light), and that index of refraction mathematical descriptions are of light as each ion in a dielectric crystal has a of a solution depends on the index of a sinusoidal wave. The relations between characteristic optical refractivity (by refraction of the end-member components electricity and magnetism derived in 1864 virtue of the number of and density of (e.g. water and alcohol), functional by James Maxwell generated not only a electrons), a characteristic radius (by electromagnetic equations could only be simple formula for the speed of light, but virtue of the atomic-electric structure) and found by assuming an average index of also allowed a description of light as a a characteristic atomic weight (by virtue refraction for materials. In wave theory, a plane-polarized electromagnetic wave. of the number of protons and neutrons), uniform wave-front cannot be maintained This wave contains a negative electric the net values of n and D calculated if each ion has a unique index of component that alternates further along in as a simple sum of the ionic properties refraction. If light is refracted by each ion, space with a positive electric component, agrees rather well with measurement (see light must consist of particles.

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The refraction of light by garnet depends on both composition and structure

From the wave theory of light, electromagnetic energy and vice-versa, the ion presents a spherical distribution of transmission through a gem occurs as so the photon has wave properties only charge to a photon that is incoming from the electric component of light induces on trace over time. This reduction of any direction, the characteristic refractivity 3 an oscillation in the electrons of the symmetry from a plane wave requires of this free ion (si = kiAW/An in nm ) is material. Much of the refraction is thus an electric-charge monopole, alternating considered to represent the refractive attributed to the loosely-held valence over time from positive to negative, with volume of the ion. electrons of the anions, as these are the polar loops of dipole magnetic ﬂux that The electric force F on a charge most polarizable. However, calculations of are perpendicular to the electric-charge near the ion varies with distance d in index of refraction based on polarizability monopole (Figure 1). proportion to 1/d2, but Coulomb's law (in nm3; e.g. the Lorentz-Lorenz equation; Refraction occurs as this local photon (of F α 1/d2) lacks subtlety. The ions Mg2+ Jaffe 1988, Eggleton 1991, Iksander 1992) is acted on by the electric charge about and Fe2+ in MgO and FeO are considered are poor because cations are also major each ion. Refraction thus occurs by serial identical because d is measured from the contributors to the index of refraction. displacement of the photon about each centre of charge (effectively the nucleus), The theory of electromagnetism also ion in the crystal structure as the photon but these ions have differences in electric lacks connections to mass. It is known, takes a roller-coaster ride through the structure that shield the charge of the however, that charge is maintained by gem. The index of refraction is due to nucleus to different degree. The ions reduction of rest mass when particles of an increased path length rather than a differ in refractivity. The working solution opposite charge form electric bonds. The reduced wavelength. In this analysis, no used here is to consider refractivity due mass of hydrogen is less that the mass new laws of physics are required although to ionic charge as Coulomb-like, with of the electron and proton alone (this new principles are introduced, and a the si of an ion affecting other ions in is the binding energy E = mc2), as mass simple equation for photon refraction then proportion to 1/d2. Σ is consumed to maintain charges of -1 indicates the composition and structure of For the equation n/D = (kidi) applied for the electron and +1 for the proton. the material. to a simple binary series such as (Mg,Fe)

Applying such ideas to light, and requiring O, by knowing n, D and di from analysis, local mechanisms of propagation (by A relation between optics, it is easy to find relative values of molar rejecting the mysterious process of action refractivity k for Mg2+, Fe2+ and O2- that composition and crystal i at a distance required for waves), a local structure exactly return the measured values of decline in the electromagnetic energy n and D. However, these values of k From atomic theory, ions form from i of a photon requires an exchange with generate inexact values of n and D in neutral elements by the gain or loss of mass (Figure 1). For a local photon, other polymorphs of (Mg,Fe)O, probably electrons. The elements Mg and O react to the electromagnetic energy of a packet due to differences in the structure-type form an ionic bond with Mg2+ and O2- ions of light oscillates with mass, if the total (Eggleton, 1991). in an MgO molecule, as both ions gain energy is constrained to a finite region One may also find relative values of an electric structure like that of an inert of space. Mass is zero for maximum k for Mg2+, Fe2+, Mn2+ and Ca2+ in garnet gas. The two positive charges of Mg2+ can i that give minimal differences between be considered to extend with spherical calculated and measured values of n and symmetry from the surface of an inert-gas D for all samples in the quaternary space core of electrons (Ne). The two valence of the (Mg,Fe,Mn,Ca) Al Si O solid electrons of O2- are held in orbital paths 3 2 3 12 + time solution, but these k values give inexact by the positive charge of the nuclear i results when applied to the broader protons, but are also attracted to the Mg2+ (Mg,Fe,Mn,Ca) (Al,Fe3+,V,Cr) Si O N cation. 3 2 3 12 solid solution, again probably due to In liquids and solids, the cations differences in structure. attract coordination polyhedra of anions Workers in mineral optics have sought and vice-versa. However, as ions of like constant values for the molar refractivity charge repel one another, paths through of oxides (Mandarino, 2007), suggesting the structure of a dielectric solid consist of a characteristic electric structure for ions Figure 1. A model of a local photon. Over one- alternating cations and anions. The regular or molecules, but a general relation quarter of the wavelength, the electric-charge grid-like arrangement of cations in crystals between optics, composition and structure monopole increases from zero to a maximum relates to near-equal forces of repulsion value, in phase with dipole magnetic flux. The must also account for birefringence. The between cations, but the valence electrons electromagnetic energy is conserved by exchange effective refractivity of an ion has been of O2- glue the structure together. with transient mass; the mass is zero when the shown to vary depending on the general In the present theory of refraction, electric-charge monopole is at a maximum. The structure-type (Eggleton, 1991) and photon maintains constant speed and momentum a single ion of Mg2+ can do work on a on variation within a specific structure and exhibits a sin2θ wave on trace over time. passing photon to change its direction. As (Teertstra, 2005). Page 107 The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

The refraction of light by garnet depends on both composition and structure

Table II: Values of refractivity (si ), cut-off distance (dc), radius of refraction (R) and radius structure refinement, the composition is (r) of free ions. determined by the scattering factors of the ions, and also by the inter-ionic distances Ion s (nm3) dc (nm) R (nm) r (nm) R/r i if the scattering factors are similar (e.g. Mg2+ 0.02158 0.38 0.174 0.089 1.9 and distances in nm for 2+ Fe 0.03130 0.42 0.196 0.091 2.2 Al-Si solid solution at a site). The density Mn2+ 0.03200 0.43 0.197 0.098 2.0 Σ calculated by refraction, D = n/ (kidi), 2+ Ca 0.03436 0.43 0.202 0.112 1.8 where di = aiAW/V = wi (the ion weight Al3+ 0.00168 0.30 0.074 0.053 1.4 fraction), must agree with the density Fe3+ 0.02680 0.58 0.186 0.065 2.9 calculated by diffraction; that is, the value k is a refractive factor analogous to the V3+ 0.02170 0.60 0.173 0.064 2.7 i ionic X-ray scattering factor. Cr3+ 0.02130 0.64 0.172 0.062 2.8 The refractivity of ions is explained 4+ Si 0.01400 0.50 0.150 0.026 5.8 entirely by classical electrostatic theory, as O2- 0.02500 0.50 0.181 0.140 1.3 the charge of each ion acts on the photon by the Coulomb force. If the refractivity The present theory uses visible-light The structure factor is proportional to the electric force, it refraction data and compares this to the The idea of photon refraction by must fall off as 1/d2. With the inter-ionic X-ray data for thin-sheet diffraction. The individual ions naturally arises because distances di known from the crystal density calculated from X-ray diffraction the volume of refraction of an ion is structure (Novak and Gibbs, 1971), values measurements is D = Σ(a AW)/VAn, where similar to the ionic volume (Shannon and i for the ionic refractivity can proxy for the a number of atoms a of type i and atomic Prewitt, 1969). Also of interest, Table II electric force. With reference to Figures 2 weight AW (g/mol) occupy the unit-cell indicates that the refractivity of a free ion and 3, the explanation is as follows. volume V (nm3). From single-crystal is a function of charge and radius. If the refractivity of a free (unbound) 2+ 2+ single ion of Mg is, say, si(Mg ) = 2, and 2- say si(O ) = 6, then the net refractivity of the MgO molecule will increase as the inter- ionic distance (di) decreases (once the ions 4+ charge are close enough to bond). This requires di < dc, where dc is a cut-off distance beyond nucleus which the refractivity of one ion does not Si measurably affect the refractivity of a distant neighbour. The inter-ionic distances di are taken from the structure data of Novak and Gibbs (1971), but one must iterate to find the dc values for each ion. photon The ion O2- places charge at Mg2+ a electric-charge θ d distance di away, and this increases the monopole ' 2+ 2+ refractivity of Mg by si (Mg ) = si(Mg ) + s (O2-)(dc – di)2. A high estimated s of 2+ charge outer-shell electron(s) i i O O2- means that it places sufficient charge of O2- at ~0.13 nm nucleus at Mg2+ to increase the refractivity of core ele Mg2+ from 2 to an effective value of, say, n ct 2- charge o ro e n ' 2+ n s si (Mg ) = 2.6, but with a low refractivity 2+ ' Mg of Mg , the effective refractivity si of nucleus O2- in the Mg-O bond may be only 6.02. Now if a second ion of Mg bonds to the MgO molecule, it will further increase the effective refractivity of O2- but will decrease the effective refractivity of Mg2+ (due to repulsion). But if the bond is Figure 2. A generalized model of the relations between the polarization of light, the refractivity and stable, n (Mg-O-Mg) > n (Mg-O). identity of ions, and inter-ionic distances and angles. The model is applicable to aperiodic molecules, liquids and solids, and crystals. The force on a photon near an ion depends on the distances and Now suppose that Fe partly substitutes angles to surrounding ions. into the Mg site. A fractional site

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The refraction of light by garnet depends on both composition and structure

on the photon is at a maximum value for Table III: Site structure factors for end- s max. i ions above and below the electric-charge member species of garnet. radius of monopole of the photon, and is zero refraction Species CX CY CZ for ions perpendicular to the proposed pyrope 0.00792 0.00877 0.01041 s monopole. For garnet, it is convenient i almandine 0.00757 0.00808 0.00938 to calculate the angle θ by considering 2 spessartine 0.00732 0.00769 0.00891 1/d polarized light refracting along an a axis. The sum is taken for all ions in a sphere grossular 0.00677 0.00592 0.00828 0 andradite 0.00373 0.00649 0.00535 0 di dc surrounding the site of interest; it is not with reference to a plane of polarization goldmanite 0.00443 0.00654 0.00615 Figure 3. Ion refractivity s vs. cut-off distance dc. i exhibited by a wave of light. uvarovite 0.00296 0.00576 0.00453 If a photon refracts at a specific level of energy The general structure-factor for at a radial distance from the nucleus, the charge Σ θ 2 specific identity of ions in a plane only refraction is C = [cos fsi(dc – di) ], beyond that radius of refraction falls off by influences the intensity of reflection. 1/d2. An ion contributes a fraction of its where f is the fractional site occupancy Any structure proposed to explain the refractivity s to a neighbour at di, also falling of ion i (accounting for solid solution), i refraction data need not be periodic (i.e. off as 1/d2. Beyond the cut-off distance dc, θ is the angle between an ion and the the ion does not contribute to the refractivity electric monopole of the photon (in this crystalline), thus allowing the photon as of a neighbour. Increasing the cut-off distance case parallel to the a axis of garnet), dc a probe of aperiodic materials including (from solid curve to dashed curve) is equivalent is the cut-off radius beyond which the molecules, glass or liquids. to increasing the radius of refraction; more With reference to the structural charge is placed at di and the refractivity of the refractivity of one ion does not affect the formula X Y Z O of the anhydrous neighbouring ion is increased. refractivity of another ion, and di is the 3 2 3 12 inter-ionic distance. Knowing n, D and the isotropic species of garnet, a photon inter-ionic distances for each composition, undergoing local refraction about an ion in the X-site has a degree of refraction occupancy (f) is needed to account for the and calculating cosθ from the structure, that is dominated by the X-cation, but solid solution, such that Mg + Fe = 1 for there are only two variables for each the refractivity is influenced by all the full occupancy of the site. For example, ion, si and dc (Table II). However, these surrounding ions (mainly by the nearest the site may contain 20% Fe, giving f(Mg) two variables are constrained to fall off ions of oxygen, but also by the more = 0.8 and f(Fe) = 0.2 for the formula as 1/d2 from free to bound cations and distant X-, Y- and Z-site cations). The (Mg Fe )O. must explain the n and D values of all 0.8 0.2 X-site contains large divalent cations in Experimentally, the electric vector of members of the solid solution. The system a distorted cube of coordinating oxygen the photon is given a known direction is thus highly constrained and strongly anions. The Y-site contains trivalent by passing the light through a polarizing convergent on specific values of si and dc. cations in octahedral coordination, and filter such as Polaroid. Attempts to Note that the structure factor for the Z-site contains tetravalent cations in describe the refraction of light through refraction is different from the structure tetrahedral coordination. Each oxygen a crystal by reference to a plane wave factor for diffraction. The physical ion is coordinated by one Z-cation, one of light were unsuccessful. If a local phenomenon affecting refraction is the Y-cation and two X-cations (Novak and photon is considered, a single value for identity of an ion that is (for a time) Gibbs, 1971). the refractivity of an ion occurs if the dominating the local refraction of a For example, the structure factor for refraction of a photon is dominated by photon; one must also account for the the X-site is the sum C = C – C – that ion over the time when the photon is distance and angle to all ions surrounding X XO XX C – C . For pyrope, Mg Al Si O , this near the ion. The refractivity is changed to this ion that alter its refractivity. By XY XZ 3 2 3 12 is C = Σ[cosθ fs (O2-)(dc – di)2] - Σ[cosθ minor degree by charge placed at the ion contrast, diffraction results from the sheet X i fs (Mg2+)(dc – di)2] - Σ[cosθ fs (Al3+)(dc – by surrounding ions. This additional force arrangement of ions in a crystal, and the i i

Table IV: Values of molar refractivity (ki) of ions in end-member silicate garnets. Species Mg2+ Fe2+ Mn2+ Ca2+ Al3+ Fe3+ V3+ Cr3+ Si4+ O2- pyrope 0.7310 0.4223 0.4376 0.6349 0.2332 0.3511 0.3359 0.3220 0.5234 0.4383 almandine 0.7223 0.4181 0.4338 0.6298 0.2185 0.3535 0.3386 0.3229 0.5001 0.4529 spessartine 0.7156 0.4156 0.4310 0.6256 0.2092 0.3541 0.3359 0.3212 0.4904 0.4636 grossular 0.6980 0.4106 0.4259 0.6196 0.1687 0.3439 0.3218 0.3091 0.4790 0.4860 andradite 0.6205 0.3772 0.3916 0.5726 0.1816 0.3503 0.3282 0.3159 0.4250 0.5494 goldmanite 0.6180 0.3758 0.3905 0.5712 0.1863 0.3529 0.3309 0.3183 0.4231 0.5443 uvarovite 0.5890 0.3634 0.3779 0.5536 0.1653 0.3425 0.3199 0.3073 0.3930 0.5766

Page 109 The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

The refraction of light by garnet depends on both composition and structure di)2] -Σ[cosθ fs (Si4+)(dc – di)2]. If s(Mg2+) Accounting for changes in density, i i References = 0.02158 and C = 0.00792 (Table III), the resultant of the k matrix is an easy- X i Eggleton, R.A., 1991. Gladstone-Dale the effective refractivity s ' of Mg2+ in the to-use formula: n = 1.714 + 0.0066667 i constants for the major elements X-site is 0.02950 nm3 and k(XMg2+) is Ca + 0.0286667 Mn + 0.0386667 XFe2+ + i in silicates: Coordination number, 3 Y 3+ 0.7310 cm /g (Table IV). The substitution of 0.077500 Fe + 0.05000 V + 0.065500 Cr. polarizability and the Lorentz-Lorenz another X-cation for Mg increases the size This formula was used to verify the values relation. Can. Mineral., 29, 525-32 of the unit cell and increases the , of n used in Table I (Teertstra, 2006) in Gladstone, J.H., and Dale, T.P., 1864. , and distances and that a linear best fit is attained between Researches on the refraction, dispersion 2+ the effective refractivity of Mg decreases. calculated and measured values of n for and sensitiveness of liquids. Phil. Trans. With the refractivity contribution of an ion numerous compositions of garnet reported Royal Soc. London, 153, 317-43 constrained to fall off as s(dc – di)2, only in the literature. i Iksander, M.F., 1992. Electromagnetic the specific values of s and dc will return i Fields and Waves. Prentice-Hall, the measured values of n of Table I. The Practical implications Englewood Cliffs, New Jersey calculated values of n are not reported The optical properties of materials Jaffe, H.W., 1988. Crystal Chemistry and because the equation is sufficiently accurate are essential to their identification. Each Refractivity. Cambridge University Press, to match the measured values of n for all proposed structural formula implies a Cambridge species of garnet in the (Mg,Fe,Mn,Ca) 3 specific state of cation order and definite Mandarino, J.A., 2007. The Gladstone-Dale (Al,Fe3+,V,Cr) Si O solid solution. 2 3 12 physical properties for gems and minerals. compatibility of minerals and its use The molar values of refractivity Using the values of si and dc in Table I, in selecting mineral species for further reported in the matrix of Table IV include the physical properties of any proposed study. Can. Mineral., 45, 1307-24 the structure factors. From the structural ionic structure may predicted (e.g. spinel, Novak, G.A., and Gibbs, G.V., 1971. The formula and relative to end-member olivine, pyroxene, glass). The method crystal chemistry of the silicate garnets. pyrope, the calculated unit-cell edge is of optical analysis is sensitive to light Am. Mineral., 56, 791-825 a = 1.1459 + 0.0130667 Ca + 0.005400 elements that cannot be analyzed by Rocquefelte, X., Goubin, F., Koo, H.-J., X 2+ Y 3+ Mn + 0.0022333 Fe + 0.010350 Fe + electron microprobe. Once values for the Whangbo, M.-H., and Jobic, S., 2004. 0.010950 V + 0.007250 Cr nm, and V = refractivity of ions are known, given a Investigation of the origin of the 3 a . For pyrope, the ionic weight fractions composition, the method can also be used empirical relationship between refractive (or fractional densities) calculated from to predict the structure. index and density on the basis of first the formula Mg Al Si O are 0.1809 Mg, 3 2 3 12 If the index of refraction and the principles calculations for the refractive 0.1339 Al, 0.2090 Si and 0.4762 O, Σ1. density or the unit-cell-volume are indices of various TiO2 phases. Inorg. With eight formula units in the unit cell measured, the values of ki may be used Chem., 43, 2246-51 volume, the formula weight is 403.127 to determine the structural formula and Rocquefelte, X., Jobic, S., and Whangbo, 3 g/mol and the density is 3.5591 g/cm . hence the composition of a garnet sample. M.-H., 2006. On the volume-dependence The calculated index of refraction is n Convergence on the correct formula of the index of refraction from the = D[(0.1809)(0.7310) + (0.1339)(0.2332) occurs as differences across the equality viewpoint of the complex dielectric + (0.2090)(0.5234) + (0.4762)(0.4383)] = Σ Σ n/ (kidi) = (aiAW)/VAn are minimized. function and the Kramers-Kronig 1.714. For minor to trace quantities of Mn, If the composition is measured relation. J. Phys. Chem., 110, 2511-14 X 2+ Y 3+ Ca, Fe , Fe , V and Cr, one may use the along with n, and the formula shows Shannon, R.D., and Prewitt, C.T., 1969. k values for these ions in pyrope. Σ Σ i X>3 and Y<2, then a recalculation of Effective ionic radii in oxides and The k values of the ions vary Y 3+ X 2+ i Fe from Fe may be verified by an fluorides. Acta Crystallogr., 25B, 928-9 depending on the identity of and the improved agreement between calculated Teertstra, D.K., 2005. The optical analysis distance to the surrounding ions. From and measured values of n. The index of of minerals. Can. Mineral., 43, 543-52 pyrope to almandine, for example, there refraction is sensitive to the valence of Teertstra, D.K., 2006. Index-of-refraction 2+ is a linear change in k(Mg ); this is an ion and to the order of cations in the and unit-cell constraints on cation X 2+ (0.7223-0.7310)/3 per Fe , and this is structure. valence and order in garnet. Can. an additional (0.7223-0.6180)/2 per V for Mineral., 44, 341-6 a hypothetical ferroan goldmanite. From the structural formula and relative to end-member pyrope, the calculated molar refractivity of Mg is k(Mg2+) = 0.7310 - The Author 0.011000 Ca + 0.0051333 Mn + 0.002900 XFe2+ + 0.055250 YFe3+ + 0.056500 V + David K. Teertstra Euclid Geometrics, 509.5 Morningside Drive, Albuquerque, New Mexico, 87108, U.S.A. 0.007100 Cr. The other k values may be i email: [email protected] calculated in a similar manner.

Page 110 The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

Ornamental variscite: A new gemstone resource from Western Australia

Margot Willing, Susan Stöcklmayer and Dr Martin Wells

Abstract: Variscite (AlPO4.2H2O) is an uncommon bluish-green mineral that has been used as an ornamental gemstone since the Neolithic Age. A new location of variscite has recently been investigated on Woodlands Station, Western Australia. The variscite from here occurs in a variety of aggregated habits within fi ne-grained Proterozoic siltstones and breccias. Rock surfaces have been found encrusted with microcrystals of variscite and wardite. Within the host rocks, associated minerals include metavariscite, crandallite, jarosite, quartz and grains of native gold. The gemmological properties of the Woodlands variscite are: RI range of 1.570 to 1.582, and SG from 2.49 to 2.55, and these are within the ranges of variscite from other world sources. X-ray diffraction analysis confi rms the variscite to be of the ‘Meßbach-type’ in association with metavariscite, a dimorph of variscite. Using visible refl ectance spectroscopy, trivalent chromium was verifi ed as the main chromophore responsible for the colour. Minor vanadium is also present, probably in mixed oxidation states of +3 and +4. Keywords: Gold inclusions, ‘Meßbach-type’ variscite, metavariscite, trivalent chromium, Woodlands Station, Western Australia

Introduction Germany where it occurred at Meßbach its dimorph — metavariscite. It is found Ornamental variscite is bluish green in quarry, Altmannsgrün, near Plauen, as veins and nodular encrustations within colour, fi ne grained and massive in habit. Vogtland, formerly Variscia (Dana, and on a variety of rock types. It may Its colour ranges from white, through light 1892). This fi nd was not a source of occur as a replacement mineral having brown and bluish-green to yellowish- ornamental grade material. In Querre’s developed in situ from phosphate-bearing green. When used together with its matrix words: “Lacroix, the famous French fl uids in association with fi ne-grained minerals and associated relict host rock, geologist, determined in 1896 the formula and clay-bearing aluminous rocks. It is the resulting reticulated patterns are of variscite, offi cial name of this mineral also reported having formed at ambient reminiscent of the variations in colour and [AlPO4.2H2O]” (Querre et al., 2007). temperature with other phosphate textures shown by turquoise-in-matrix. Variscite also occurs as microcrystals minerals within soils and on various Variscite has characteristics common with that are recorded as colourless, green or substrates including serpentinite derived turquoise, the best-known ornamental red. The rare ferroan red variety occurs by chemical action from bird guano phosphate gem mineral. They are as encrustations on hematite at Iron (Simpson, 1952). recorded together in some worldwide Monarch quarry, Iron Knob in South History of early exploitation (4500–3000 localities and the mining history of both Australia and at Boa Vista mine in Minas BC) of variscite from the Iberian Peninsula minerals dates to the Neolithic Age. Gerais, Brazil (http://www.mindat.org/). is reported from recent archaeological Variscite, a hydrated aluminium Variscite forms at low temperature as a work (Arribas et al., 1970, Harrison et al., phosphate (AlPO4.2H2O), was fi rst secondary mineral commonly associated 2001; Camprubi et al., 2003; Dominguez- described in 1837, from a source in with other hydrated minerals particularly Bella, 2004), where evidence at some sites

Ornamental variscite: A new gemstone resource from Western Australia

c a

Figure 1a: Variscite seahorse on quartz base, height 20 cm. Carved by Robert Jüchem, Idar-Oberstein, Germany. Figures 1b and 1c: Gold mounted pendant (30 mm diameter) and gold-mounted cufﬂinks (17 mm square), fashioned by Murray Thompson, Goldsmith, Brett Barker. indicates workings continued to be mined Tooele County (Doelling, 1980). The state Terminology into the Middle Ages. Variscite jewellery in of Nevada has also been a source for gem the form of beads, necklaces and pendants variscite, with the Verde Web variscite Minerals is recorded from numerous Neolithic sites mine in Lander County (Novak, 1982) Metavariscite: monoclinic; dimorph of in Spain and Portugal, from burial sites in being one recorded producer. variscite.

France (Forde, 1930) and, more recently, Variscite of blue green colour and Strengite: orthorhombic; Fe PO4.2H2O, from rare Roman (AD 43–410) sites in translucent quality suited for ornamental forms an isomorphous series with England (Middleton, 2007). purposes (Figure 1) is being mined from variscite; Fe3+ replacing Al3+. Most of the ornamental variscite a new location at Woodlands Station in Variscite: orthorhombic; a member of a used in modern times for lapidary and remote Western Australia (WA). Recent mineral series that includes arsenates jewellery purposes has originated from research has established that elemental and phosphates with the general formula

finds in the U.S.A., notably Utah. Deposits gold occurs as inclusions within this AXO4.2H2O, where A = aluminium from here, first discovered in 1893, variscite (Hancock, 2008). Although (Al3+), iron (Fe3+), chromium (Cr3+) or have been worked sporadically into the variscite is recorded from other locations indium (In3+) and X may be arsenic (As) mid-twentieth century (Larsen, 1942; within WA it has only been mined or phosphorus (P). Two polymorphic Dickerson, 1971). Clay Canyon in the previously from Milgun Station, south east varieties of variscite exist: ‘Meßbach’ (VM) Oquirrh Mountains, Fairfield County, Utah, of this new find. and ‘Lucin’ (VL) types, closely related, has been the largest producer (Thomssen, In this paper, the authors describe differing only in unit cell dimensions. 1991) with other occurrences including the properties of this new ornamental Both terms are derived from their the Little Green Monster, and Utahlite variscite, its geological occurrence and localities in Meßbach, Vogtland, Germany Hill, Box Elder County and Amatrice Hill, associated minerals. and Lucin (Utah, U.S.A.); see Clark (1993).

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Ornamental variscite: A new gemstone resource from Western Australia

Historical mining and uses of variscite

Early to Middle Stone Age (c. 4500–2500 BC) Exploitation of variscite as an ornamental material dates to prehistory. It was desirable, favoured for its intense green and blue-green colour. It was also of value as shown by the efforts made by Neolithic peoples to mine, fashion and trade it over hundreds of kilometres through parts of Europe. Recent archaeological work, notably at Can Tintorer in the Gavà Neolithic Mining Complex, about 20 km SW of Barcelona in NE Spain shows the early and deliberate exploitation and mining of variscite from 4000 BC over a period of 300-400 years (Harrison et al., 2001). Veinlets and seams of variscite were worked from host rock slates via underground passages and galleries covering hundreds of metres, to depths of 40 m (Camprubi et al., 2003). Beads and other items (Figure 2a) were fashioned in settlements nearby and exchanged across Spain and into the Pyrenees, distances up to 550 km.

Figure 2b: Variscite pendant and beads from burial sites in Mané-er- Hroëk, Brittany, France (4500-4000 BC). British Museum collection, with permission.

north-western France, notably Neolithic tombs at Lannec-er Ro’h and Mané-er-Hroek, Morbihan, Brittany (Forde, 1930; Cassen, 1998). Recent trace element analyses of green beads and pendants from these burial sites indicate that the original source of the variscite is from the Iberian Peninsula (Querre et al., 2007). An item of this collection, housed in the British Museum is a pendant fashioned from one piece of variscite and measuring 45 mm x 29.5 mm (Figure 2b). The collection of ten beads displays various qualities of variscite, but overall the colours are intense, the beads well polished, the shapes varying between ovoid, discoidal and cylindrical with two showing several sets of bevels or facets, and all unornamented. The largest has a length of 21 mm. All are drilled through for suspending with large diameter holes, from 2 to 4 mm. These worked variscite articles have previously been described under the terms ‘Callais’ and ‘Callainite’ (Bauer, 1904), and it is possible that other archaeological ﬁnds of green ornamental materials may include variscite that has not yet been veriﬁed Figure 2a: Variscite collar necklace found in a burial site inside the mineralogically. Neolithic mines of Gavà, Spain.

At Palazuelo de las Cuevas, Zamora, west of Can Tintorer, The Roman Period (AD 43–410) the mining of variscite also dates to the fourth millennium Rare ﬁnds of variscite beads and jewellery are also known BC and beads from these two areas do not overlap in their from the Roman era, and some examples from Britain are trading. Variscite from here was also exploited in the later listed in Table I. In contrast to the large numbers of beads Roman period (Dominguez–Bella, 2004) and into the Middle dated from the Stone Age period, those attributed to the Ages (Arribas, 1970). Similar mining and bead trading is Roman era are uncommon. known in parts of Portugal, where hundreds of beads have These rare archaeological ﬁnds demonstrate the importance been discovered (Meireles, 1987). and high esteem associated with owning variscite jewellery. Beads and pendants of variscite of various sorts and styles The source of the variscite found in these Roman deposits has are also known and described from the Carnac region of not been established with certainty.

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Ornamental variscite: A new gemstone resource from Western Australia

Table I: Variscite artefacts found at archaeological sites in Britain; all Roman Period (AD 43-410).

Variscite artefacts Archaeological sites Reference Fragment of a ring shank; carved in criss-cross Gadebridge Park, Hemel Neal, D.S. (1974) design with serpents’ head ﬁnial* Hempstead 3 x beads; octagonal cross-sections Balkerne Lane, Colchester Crummy, N. (1983) 1 x bead; octagonal cross section Tanner Row, York Hooley, D. (1988) 1 x bead; faceted cuboid Rougier Street, York Hooley, D. (1988) Unpublished Ref. in Middleton et al. (2007) 7 x cylindrical green beads; mounted on an Grange Farm, Gillingham, Kent Middleton et al. (2007) incomplete gold necklace

* The ﬁrst record of variscite identiﬁed from an archaeological site in Britain

Common misnomers • Utahlite: a trade name for compact quality that has been exploited worldwide • Amatrice or amatrix: a trade name, variscite nodules from Stransbury with an intense bluish-green colour and a coined term to describe variscite Mountains of Tooele County, Utah. translucent quality. Some of the material together with matrix material; also • Variquoise: a trade name describing occurs with textural characteristics that referred to as American matrix and combined variscite and turquoise rock make sculptural objets d’art attractive and variscite-quartz. Amatrice commonly • Verde web variscite: a trade name for recognizably different to variscite from includes wardite within its occurrence light blue and light green variscite with elsewhere. The new deposit outcrops as concretionary masses. included black ‘spider web’ pattern sporadically over a distance of several • Callais, callainite: obsolete mineral matrix, from Lander County, Nevada. kilometres and has potential to be an names, originally terms describing For more on variscite names, see important source of gem- and carving- turquoise and attributed to Pliny. These Dietrich (2008). quality material. Until these recent new terms also have described non-specific finds, the only previous mining of variscite green ornamental materials from Variscite from Western in Western Australia was on Milgun ancient grave sites in Brittany. Both Australia Station, located 67 km southeast of the turquoise and variscite have been so Variscite from the new occurrence ‘Woodlands’ deposit. described in archaeological studies and in Western Australia was first shown in During a period from the early 1980s early mineral reference works. 2006 at the Arizona Mineral and Fossil until 2001 several mining companies were • Lucinite: a trade name for variscite from Show in Tucson (Laurs et al., 2007). The active in the general area searching for near Lucin, Utah. material is comparable to the highest gold and various base metals. Variscite was recorded in drill samples from several locations on Woodlands Station during this time. This historical information was later followed up and more recent detailed prospecting has established several areas where variscite occurs. The variscite described in this paper is from the first new discovery that was made in 2004. Located within the 1:250 000 Western Australian Geological and Topographical map series Sheet SG 50 -3 (Mt Egerton), it is situated on Woodlands Station (Figure 3) within the Shire of Meekatharra, approximately 1000 km north of Perth and 95 km east south east of Mount Augustus. The most direct access is off the Mt Augustus/Woodlands road that intersects the Great Northern Highway a Figure 3: Woodlands Station variscite deposit, Western Australia; view northwards from the mine site. few kilometres north of Meekatharra. Foreground shows mined ore.

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Ornamental variscite: A new gemstone resource from Western Australia

Geological setting All the new occurrences of variscite on Woodlands Station, as well as those from sources on Milgun Station, occur within sedimentary rocks that form part of the Mesoproterozoic Bangemall Supergroup, dated at 1000–1600 Ma. The most recent occurrences are from argillaceous sediments and silicified breccias of the upper Kiangi Creek Formation, part of the middle Edmund Group. The Kiangi Creek Formation comprises predominantly terrigenous sediments, especially arenites, and fine-grained brown and grey shales, and silt-, mud- and claystones, with minor Figure 4: At the mine site. Specimen boulder showing variscite veining. horizons of cherts and dolomites including a stromatolite horizon. The original 2008). Individual stratabound variscite here, was collected from loose samples sediments were accumulated on a marine seams range from a maximum width of at the ore heap, augmented with selected shelf, with restricted current circulation ~55 mm to more common widths of <20 specimens donated by the mine owners. under hypersaline conditions (Muhling mm; seams also interconnect with one and Brakel, 1985). another via narrower veins (Figure 4). Nature of the variscite Variscite occurs as conformable seams In some veins variscite has a markedly The variscite is varied in its nature within brown siltstones and as cross- fibrous nature occurring in cross-fibre and colour; that exploited for decorative cutting veins and irregular zones within orientation to the general bedding of the and gemmological purposes is brecciated chert and silicified siltstone host rocks. Elsewhere, the host rocks have microcrystalline, intense green in colour horizons. Quartz veining is commonly been brecciated and cross-cutting veins of and commonly microfibrous in habit. associated with variscite where the host variscite both traverse and enclose angular There is wide variation in occurrences of rocks are brecciated. rock fragments. Veins may be less than this fine grained variscite; from the seams 1 mm wide and connect with irregularly already described that are fairly regular Field occurrences shaped zones several centimetres across; in width, to contorted and ‘ptygma’-like Occurrences of stratabound variscite however only one open-cut has so far veins with folds that pinch and swell have been traced in the host rocks along been progressed and all the material (Figure 5a). In other specimens variscite strike for approximately one kilometre described is from this site. The open- occurs as globular and botryoidal and zones containing nodular and cut is ~30-40 m in length and has been aggregations and, unusually, in tapered veinlet forms of variscite have been mined only during short periods in the pod-like aggregations (Figure 5b). Rare found over a larger area. The horizon wintertime, so far yielding several tonnes encrustations of microcrystals of colourless containing the variscite veins varies of material. At other times, the quarry variscite (Figure 5c) and wardite (Figure between approximately 400 and 900 mm site is temporarily covered with spoils 5d) were identified on rock surfaces and in thickness (D. Vaughan, pers. comm., material, and the variscite, as described in fillings of small cavities.

a b

c d

Figure 5: (a) Blue-green variscite-in-matrix showing ‘ptygma’-like veining. (b) Vein of pod-form variscite with brown rock matrix. Seam thickness ~35 mm. (c) Rock surface — encrustations of secondary minerals; dominantly colourless variscite crystals. Centre: crystal of variscite (0.5 mm). (d) SEM image showing wardite crystals as an encrustation on siltstone.

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Ornamental variscite: A new gemstone resource from Western Australia

Material and methods Samples of gem-quality variscite were cut using a 0.35 mm diameter diamond wire saw, and sections of four specimens V1, 4–6 are shown in Figure 6a. Standard gemmological methods were used on a selection of fashioned cabochons and carvings (Figure 6b) to determine refractive index (RI), specific gravity (SG) and luminescence. The absorption spectrum was captured with a digital camera attached to a monocular microscope which housed a diffraction grating spectroscope. Internal features were examined through a binocular microscope with oblique illumination. Petrographic thin sections were prepared to view the relationship between country rock and the variscite mineralization through a standard petrological microscope. Further mineral identification work was assisted by RI oil-immersion techniques on grain Figure 6b: A composite image of a selection of gem-quality ‘Woodlands’ variscite cabochons and carvings. Specimens top left and top right carved by Dalan Hargrave; oval and rectangular crushes. Due to the very fine-grained cabochons fashioned by Murray Thompson. nature of the minerals it was necessary to confirm all identification work with A Philips XL40 Controlled Pressure MagiX PRO XRF equipped with a scanning electron microscope (SEM) SEM fitted with an EDAX energy 4.0 kW tube with fixed channels for Al and X-ray diffraction (XRD) techniques. dispersive X-ray spectrometer (EDS) and Si. Detection limits for most trace The XRD data were collected using and a Robinson Back Scattered Electron elements reported are ~10 ppm; major a Philips X’Pert XRD fitted with a Cu (BSE) Detector, was used to identify oxide report detection limits between tube (1.54056Å), automatic divergence gold and minerals associated with 0.002% and 0.01%. slits, and diffracted beam graphite variscite. Reflectance spectra covered monochromator with the following X-ray fluorescence (XRF) for the visible to short-wave infrared settings: 2-theta range = 5–65°, step size quantitative chemical analysis was wavelength range (400 to 2500 nm). = 0.03°, step time = 2s, divergence slit = performed on fused glass beads Reflectance spectra of the unpolished 1 mm (fixed), receiving slit = 0.8 mm. consisting of variscite mixed with and polished surface of each 20 mm The Debye Scherrer X-ray powder lithium tetraborate and metaborate in square by 1–2 mm variscite slab were (XRD) camera method was used to the ratio 12:22 as flux. The beads were measured using an ASD Field Spec® identify crystals occurring on rock measured on a sequential PANalytical Pro FR spectrometer (Analytical surfaces. Spectral Devices, Boulder, U.S.A.), optimized and calibrated against a 100% reflectance Spectralon® white reference standard. A mixed acid digest and the ICP-MS method of analysis was used for minor elements, the rare earths and Y, Th and U; Sc was analysed using ICP-optical V1 V4 V5 V6 emission spectroscopy. Figure 6a: Sections of four variscite specimens — V1,V4, V5 and V6 — used in this study.

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Ornamental variscite: A new gemstone resource from Western Australia

Results

Optical mineralogy and petrology

Host rocks Variscite is hosted within siltstones, where it commonly occurs in conformable seams, and in brecciated zones, where it may be accompanied by quartz. The Figure 7a: Brown siltstone with stratabound variscite Figure 7b: Brown siltstone hosting veins of light brown siltstones (Figure 7a) are seam (20 mm thickness) in cross-fibre habit. variscite and quartz lenses. very finely banded but non-fissile and may be locally silicified. The texture is accentuated by streaks and microlamellae of reddish-brown iron oxides that also occur as euhedral castes, probably pseudomorphs after iron pyrite. Siltstones in contact with variscite contain a high proportion of secondary minerals; including variscite, quartz, crandallite and jarosite (Figures 7b, 7c). Within brecciated Figure 7c: Thin section of limonite-clouded Figure 7d: Thin section of breccia showing zones, rock fragments are commonly siltstone, bordered by microlaminae of variscite oxidized and silicified siltstone fragments in silicified and are distinctly harder than and crandallite (colourless). The siltstone is a microcrystalline groundmass of variscite. the siltstones. Many fragments have an speckled by granules of iron oxide-after-pyrite. Magnification 50x, cross polarized light. ultrafine ‘chert-like’ texture and may Magnification 50x, cross polarized light. appear red-brown and clouded white in occurrences and characteristic reticulate banding (Figure 8b) with sweeping reflected light; some fragments are cherts, patterns are developed in some places. plumose extinction patterns when viewed others are probably silicified siltstones These patterns have developed where between crossed polars. Variscite with (Figure 7d). Due to their fine-grained bundles of variscite fibres, in elongate these textures shows high translucency. nature (1 μ), their mineralogy could not or pod-like forms, are closely packed Especially well developed around be confirmed by optical methods. with interstitial relict rock and brown- pod borders is a distinctive pattern of coloured matrix outlining their borders polygonal brown patches (Figure 8c). Variscite and associated minerals (Figure 8a). Dimensions of pods vary; the The pattern is clearly visible in plane Variscite occurs in two distinct habits; longest measured 25 mm in the longest polarized light (PPL) and is similar to a equigranular (Figure 7d) and fibrous dimension. Pods often show variation in craquelure texture in the varnish of some (Figures 8b, 8c). Equigranular variscite the green colour at their perimeters. Thin old paintings and to that developed on with ‘salt and pepper’ ‘chalcedonic-like’ sections at greater magnification show the surfaces of septarian nodules. The texture generally occurs within narrow the fibre patterns and concentric growth texture may be the result of dehydration veins and in zones bordering rock banding within individual pods (Figures and shrinkage of pods, sometime after fragments within the brecciated zones. 8b, 8c). In longitudinal section pods show formation. Some pod borders are also Fibrous variscite dominates in seam preferred fibre orientation and concentric lobed and finely fimbriated; these may

Figure 8a: Thin slice of variscite V6 viewed in Figure 8b: Thin section of colloform variscite V5; Figure 8c: Thin section of variscite V6 — transmitted light showing a reticulate pattern of fibres have aggregated to form elongated pods, transverse sections of pods, polygonal forms variscite pods with interstitial matrix minerals. with concentric growth patterns. Magnification with reticulate pattern of interstitial remnant The variscite shows high translucency and green 50x. brown rock. Border zones of individual pods zones of different intensities are visible. show desiccation textures. Magnified 50x.

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Ornamental variscite: A new gemstone resource from Western Australia

Table II: Summary of the gemmological properties of ‘Woodlands’ variscite

Colour Light bluish-green Light to dark green Diaphaneity Opaque to translucent Lustre Waxy; takes a high polish Hardness ~ 5 Fracture Uneven RI (range) 1.570 to 1.582 SG 2.49 to 2.55 UV ﬂuorescence Inert to both LW and SW Figure 9a: The brown speckles on this host rock Chelsea colour ﬁlter Grey to pale pink response surface are crandallite. Absorption spectrum Diffuse bands ~685 nm, 650 nm, 610 nm; absorption of the blue-violet Microscopic features Gold inclusions. Matrix: clay, quartz, iron oxides.

700 650 600 550 500 450 400 nm

Ruby emission doublet

Variscite

Figure 9b: Thin section showing crandallite Figure 10: Absorption spectrum of variscite slab V4 ~2 mm thick, from a diffraction grating microspheres in clouded siltstone. Magnification spectroscope, beneath a synthetic ruby spectrum showing its emission doublet as a calibration 50x, cross polarized light. marker. be deformational features caused by extinction patterns in thin section. In occur in open veins and micro vugs close packing and folding of the pods at hand specimens some siltstones appear where comb structures are also present. the time of crystallization. The interstitial speckled due to the development of material between pods is dark coloured spherulitic crandallite. Turquoise and interconnects, accentuating the Although not visible in specimens reticulated overall pattern. It is optically Jarosite V1–V6, turquoise is reported occurring as semi-opaque and grey or brown in colour Jarosite (KFe3(SO4)2(OH)6) is a minor thin conformable veins within the host with red oxide grains. The presence component, occurring as encrustations rock (Nickel et al., in press). of alunite, kaolinite and xenotime was on, and within, the siltstones as a late confirmed using SEM; crandallite and secondary mineral and is distinctly yellow Gold quartz were identified as secondary or greenish yellow in colour. It is found A rare and unique feature of the fillings with layered growth banding; other in veinlets throughout rock fragments of variscite is the occurrence of native gold substances could also be present. the breccia as well as in fissures through as inclusions (Figure 11a). In the group zones of variscite. It occurs as lath-like of specimens examined in this study, Crandallite grains and as fibrous fan-like sheaves. In gold occurs in discrete grains, some as platelets, others as grains with spongy Crandallite (CaAl3(PO4)2(OH)5.H2O) thin section under crossed nicols it often occurs as a secondary mineral in fine displays anomalous interference colours and pelletized surface textures. Grains bands (~2-3 mm) throughout some of of ‘Berlin blue’ range in diameter from 25 μ to 100 μ. the host rocks (Figure 9a), especially Gold is most easily visible in the dark common in those in contact with variscite. Quartz green variscite, although it is also reported Grains display a range of habits: granules, Quartz is common in cross-cutting veins to occur in massive and colloidal forms fibrous sheaves and microspheroids ~25 and lenses (Figure 7b) within the country within the host rocks (Hancock, 2008). μm in diameter (Figure 9b). Crandallite in rocks and brecciated horizons, and the It occurs within the variscite as late sheaf and spheroidal forms has commonly associated variscite is often coarsely syngenetic or epigenetic inclusions. The formed along open gashes and may crystalline with hypidiomorphic granular granules are reported to be of high purity show concentric growth and sweeping textures. Well terminated quartz crystals containing no silver and may represent a

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Ornamental variscite: A new gemstone resource from Western Australia

Table III: Chemical composition of re-precipitation of primary gold that has a been reported within the sedimentary ‘Woodlands’ variscite. sequences (Hancock, 2008). Wt. % V1 V4 V5 V6 Gemmological Oxide/ characteristics b Element Al O 31.6 32.10 30.6 31.5 Appearance 2 3 SiO 0.47 1.04 0.50 1.46 The selected cabochons and carvings 2 P O 45.3 45.9 44.4 45.7 fashioned from massive gem variscite Figure 11: (a) Gold inclusions in variscite V6 2 5 TiO 0.14 0.31 0.40 0.29 (Figure 6b), exhibit light to intense green between 30 and 100 μm across. 2 Oblique illumination. 1.37 1.08 1.86 1.27 hues with some specimens showing Fe2O3 a bluish-green. Most gem variscite (b) Reticulate patterning of matrix CaO bdl bdl 0.19 0.05 material outlining variscite pods. is opaque, but portions of the dark 0.08 0.10 0.19 0.12 Oblique illumination 7x. Na2O green type show a marked degree of K O 0.13 0.02 0.06 0.02 opaque inclusions (Figure 11a). SEM-EDS 2 transparency. The brown matrix material V O 0.35 0.32 0.46 0.50 analyses of surface-reaching inclusions 2 3 provides the colour contrast in the 0.09 0.21 0.18 0.16 confirmed their identity as elemental gold. Cr O characteristic web, cellular and reticulate 2 3 SEM-EDS and XRD analyses of the brown bdl bdl 0.08 bdl patterns. PbO matrix material, forming patterns within 0.43 0.09 0.31 0.11 SO3 Optical and physical properties the variscite (Figure 11b), confirm the F 0.05 0.10 0.11 0.07 presence of iron oxides, quartz, and traces The gemmological properties of LOI* 21.90 18.50 21.90 17.20 of crandallite and alunite. the selected variscite cabochons and -O=2F - 0.02 - 0.04 - 0.05 - 0.03 carvings are summarized in Table II. RIs, Total 101.89 99.73 101.19 98.42 measured by the distant vision method on Mineral identification bdl: below detection limit cabochons, range from 1.57 for the lighter Two X-ray diffraction patterns of * The loss on ignition value (LOI at 1050°C) ‘Woodlands’ massive gem-quality variscite material, to 1.58 for mid to darker green was used to calculate total water in the material. Small birefringence was evident samples V1and V5 (Figure 12) indicate formula for V1, V4-6. on plane polished surfaces of translucent that the dominant phase is variscite. V1 (Al Fe V )Σ (P Si S )Σ dark green variscite, and RI readings Both patterns match 25-18, International 0.96 0.03 0.01 1.00 0.99 0.01 0.01 1.01 O .1.91 H O of 1.578 to 1.582, were recorded. The Centre for Diffraction Data (ICDD) 4 2 V4 (Al0.96Fe0.02V0.01Ti0.01)Σ1.00 (P0.99Si0.03)Σ1.02 specific gravity of the variscite cabochons database for the ‘Meßbach-type’ variety O4.1.6 H2O of variscite (Salvador and Fayos, 1972). varies due to porosity and composition, V5 (Al0.94Fe0.04V0.01)Σ0.99 (P0.98Si0.01S0.01)Σ1.00 O .1.91 H O from 2.49 to 2.55, the highest value Minor amounts of metavariscite (Kniep 4 2 V6 (Al Fe V )Σ (P Si )Σ O .1.6 being recorded from dark green material. and Mootz, 1973) are present in variscite 0.96 0.03 0.01 1.00 1.00 0.04 1.04 4 H O The properties of this new ‘Woodlands’ sample V5, and crandallite and alunite are 2 variscite from Western Australia are within present as traces. the ranges of published values in the gemmological literature (Webster, 1975). The absorption spectrum of the predominantly translucent variscite V4 (Figure 10), displays a Cr3+ spectrum with bands of diffuse absorption in the red at ~685 nm and ~650 nm, and an absorption cut-off below ~465 nm. A diffuse band at ~610 nm is unassigned. The Vis-NIR reflectance spectroscopy section gives a intensity V1 more detailed spectral analysis of the four V5 variscite slabs (see below). metavariscite Inclusions Microscopic examination of several 10 15 20 25 30 35 40 45 50 2-theta angle (deg) polished specimens of gem quality variscite showed planes of yellowish-gold Figure 12: X-ray diffraction patterns of variscites V1 and V5. Patterns displaced vertically for clarity.

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Ornamental variscite: A new gemstone resource from Western Australia

vanadium to chromium ratio of 2.5:1, in 350 element — ppm comparison to ratios of 2.9:1 for El Bostal, 300 and 2.2:1 for Pannéce. 250 The relatively high lead content of 750 ppm in variscite sample V5 (Table III) may 200 signify selective enrichment of isotopes 150 in the variscite and this specimen was also analysed using inductively coupled 100

Concentration (ppm) plasma mass spectrometry (ICP-MS). 50 The results are summarized in Figure 0 13 and show that the actinides, uranium Sr Ba Sc Y La Ce Pr Nd Sm Th U Mo Ga As Sb (~50 ppm) and thorium (~100 ppm), Element are in high abundance, indicating the presence of active daughter nuclides and Figure 13: Minor element content of variscite V5. related gamma radioactivity, from the natural decays of U238 to Pb206, U235 to Chemical composition it was below the detection limit (bdl); Pb207 and from Th232 to Pb208 (Senior and The ideal formula for variscite is consequently, all of the iron is assigned to Chadderton, 2007). This is consistent with AlPO .2H O. The results of quantitative the ferric (Fe3+) state. 4 2 the finding of anomalous radioactivity x-ray fluorescence analyses of four gem The vanadium and chromium contents using a portable field scintillometer in the grade ‘Woodlands’ variscite samples V1, of ‘Woodlands’ variscite (Table III) display siltstone layer below seams of variscite V4-6 are summarized in Table III. In a similar chemical fingerprint to the (D.Vaughan, pers. comm., 2008). addition to the major detectable elements variscite deposits of El Bostal – Zamora Also of note is the scandium (Sc) of Al, P and water in the ideal formula, (Spain) and Pannéce – Brittany (France), content of 100 ppm, which equates to minor amounts of Si, Ti, Fe, V, Cr and S (Querre et al., 2007, fig.1). The mean ~3oz per tonne and is similar to the are present. The elements Na, K and F are vanadium content of 2771 ppm and variscite-Sc association in Utah. In 1942, also present as traces. A separate analysis chromium content of 1094 ppm of the several hundred pounds of variscite 2+ for the ferrous ion (Fe ) indicated that four ‘Woodlands’ variscites result in a were found in the vicinity of the Utahlite mine, Utah, whilst the area was being prospected for scandium (Novak, 1982). Table IV: Absorption band centre wavelengths and band assignments in variscite. A sample of gem grade variscite Sample analysed for elemental gold by neutron V1 V4 V5 V6 Band assignment Reference activation, contained 17.5 ppm gold. Band centre (nm) 520 525 535 525 Transmission window Vis-NIR reflectance - - - 424 Fe3+ ions Calas et al., 2005 spectroscopy - 451 - - Cr3+ ν2 transition, 4A (F) 4T (F) Calas et al., 2005 2g 1g Colour properties: chromophores 631 630 629 631 3+ ν 4 4 Calas et al., 2005 Cr 1 transition, A2g(F) T2g(F) Reflectance spectra for each unpolished 655 656 656 655 Cr3+ spin forbidden transition, Balan et al., 2002 surface of the four slabbed variscite 4 2 samples V1, V4, V5 and V6 are presented A2g(F) T1g(G) Calas et al., 2005 in (Figure 14a). The relatively greater 690 690 690 690 Cr3+ spin forbidden transition, Balan et al., 2002 overall reflectance ratio (albedo) of V1 4A (F) 2E (G) Calas et al., 2005 2g g is due to its opaque nature compared to 861 855 856? 857 Vanadyl, VO2+, groups Calas et al., 2005 the other variscite samples, which are nd 886 888 887 Vanadyl, VO2+, groups (?) Calas et al., 2005 near-translucent (i.e. gem-quality). The 1179 1177 1174 1175 OH overtone? slabbed form allows transmission of some 1240 1239 1237 1239 V3+ spin forbidden transition, Alda et al., 2003 incident illumination with a corresponding 3 3 1 1 1 1 T1g( F) Eg( D), T2g( D) reduction in the overall albedo, but the wavelengths of measured absorption 1281 1279 1280 1279 Unassigned bands are not affected. NB: Band centre values are averaged from reflectance measurements for both the The main absorption activity occurs in polished and unpolished surface of each variscite slab. nd: not determined. The absorption band was too broad to accurately determine a the visible to near-infrared wavelength centre position. range from 400 to ~1500 nm (Figure 14b).

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Ornamental variscite: A new gemstone resource from Western Australia

Absorption features in the shortwave 0.8 infrared wavelength range, 1500 to 2500 630 1175 1430 978 nm, are generally weak, broad and poorly 0.7 V1 — 865 resolved. The broad band between 1460 0.6 and 1879 nm may be related to SO 4 V4 — groups of minor associated mineralogy 0.5 (e.g., jarosite), whereas the sharp feature near 1430 nm can be assigned to OH 0.4 V5 — vibration overtones of structural water 0.3 within variscite. However, the main (au) Reflectance V6 — absorption activity occurs in the 400 to 0.2 1500 nm wavelength range, and it is this region that is the focus. 0.1 Wavelengths and band assignments of 0 measured absorption features are listed 400 800 1200 1600 2000 2400 in Table IV. The transmission window/ Wavelength (nm) maximum reflectance for variscite V1 is on the edge of the green at 520 nm, Figure 14a: Reflectance spectra for the unpolished surface of four slabbed variscite samples. The sharp features at approximately 978 and 1430 nm are overtones of OH vibrations from structural whereas transmission windows in samples OH in variscite and are not listed in Table IV. Reflectance spectra have not been vertically offset. V4–V6 shift towards the mid-green at ~528 nm. Two main absorption bands were detected at 520–750 nm (centre ~630 nm) 3+ V4+ Cr V3+ Hull removed } and 750-1100 nm (centre ~865 nm); with 1 } V6 631 857 the former band related to chromium and 0.9 the latter feature due to vanadium. In 655 0.8 690 octahedral co-ordination Cr3+ shows two 887 1175 absorption bands arising from the spin- 0.7 1239 allowed ν1 and ν2 transitions at 629 and 0.6 978 444 nm, respectively (Calas et al., 2005). 1279 0.5 Whilst all measured variscite samples 0.4 show a prominent Cr3+ spin-allowed 1430 ν1 band, the ν2 transition was not fully (au) Reflectance 0.3 resolved in any of our variscite samples. 0.2 Instrument noise at wavelengths <450 nm, Reflectance 0.1 (V6) together with the increasing absorption tail near 400 nm due to ligand-metal- 0 400 600 800 1000 1200 1400 charge-transfer (LMCT) from bands such Wavelength (nm) as O-V in vanadyl and possibly O-Fe due to Fe3+ replacing Al in variscite, interfered Figure 14b: Reflectance (red curve) and Hull removed spectra (black curve) for variscite V6, showing detail of absorption features in the 400 to 1500 nm wavelength range. The Hull removed spectra and obscured the Cr3+ ν2 transition at helps to emphasize small absorption features not easily resolved in the reflectance spectrum. near-UV wavelengths. Absorption features at 978 and 1430 nm are overtones of OH vibrations from structural OH in The weak but sharp absorption features variscite and are not highlighted. The spectra have not been vertically offset. on the high wavelength side of the ν1 transition at 655 nm and 689 nm (Figure The second main absorption band, +4 or +5 oxidation states, with transport 14b) are characteristic of Cr3+ in octahedral centred at ~860 nm can be assigned to of V4+ and V5+ in the fluid state being the co-ordination (Calas et al., 2005). Their vanadyl, VO2+, groups with V in the +4 most common (Schindler et al., 2000). detection confirms the presence of Cr3+, oxidation state. Splitting of this band by Recent optical absorption spectra recorded rather than V, as the main chromophore an additional feature at 890 nm (Table IV) for variscite and metavariscite, detected in variscite (Calas et al., 2005). Similarly, produced an asymmetric broadening to only a very weak feature near 870 nm, detection of these spin-forbidden longer wavelengths. However, the smaller which was interpreted by Calas (2005), transitions in spectra measured for dickite longer wavelength feature at 1240 nm, supported by other data, as indicating 3+ 3+ 4+ also confirmed the incorporation of Cr assigned to V indicates that V in variscite little V but substitution of PO4 tetrahedra within the structure of this clay mineral may be in a mixed oxidation state. by V5+ as vanadate groups. (Balan, et al., 2002). Vanadium can occur in either the +2, +3,

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Ornamental variscite: A new gemstone resource from Western Australia

deposits are situated within ﬁ ne-grained dominantly argillaceous rocks of extensive a occurrence, where gold is known to be present. The variscite occurs together with several minor minerals, notably crandallite, alunite, iron oxides and quartz; these minerals may be present within the b ornamental grade material. Metavariscite was found to occur more commonly within pale coloured and partly altered variscite material. The presence of gold granules as co-genetic inclusions within the variscite is of great interest as a rare gemmological phenomenon and provides the prospects with added economic potential. The variscite seams are generally <100 mm wide, limiting thickness of useable material and typical examples of carved, cut and polished variscite are illustrated. Larger objects can be worked from material using other directions and incorporating matrix material. The

Figure 15: (a) Variscite carved in somewhat porous nature of variscite, contemporary freeform style; due to its ﬁ brous nature, may result in height 11 cm. Carved by Dalan discoloration if in contact with certain Hargrave, U.S.A. liquids, and tests using refractive index (b) Chinese carving of variscite in oils, for example, resulted in yellowish traditional style; height 4.5 cm. staining. The matrix material in the variscite with Discussion and summary Western Australia is now a source a reticulate pattern can be both friable Variscite as an ornamental mineral is of ornamental quality material and and porous, and like turquoise, would used in its microcrystalline and massive deposits on the Woodlands sites have need to be stabilized with wax or resins to form and has adequate hardness for considerable economic potential. The avoid accidental damage and permanent carved objects to take a good polish. Its attractive colour and appearance in complex textural patterns have contributed to its popularity (Figures 15 and 16). Although the exploitation of variscite has a long history, there have been few sources of ornamental quality material worldwide. Much of the variscite currently marketed is from stockpiled material from known and inactive occurrences principally from the states of Utah and Nevada, U.S.A. Some of this material has been collected on a casual basis from old workings, sites that are also visited by researchers and private mineral collectors. In contrast, non-gemmological low- grade variscite and microcrystals are not uncommon and are recorded from many Figure 16: Variscite ﬁ sh; dimensions 35 cm x 25 cm, ~4 kgs. Eyes fashioned from hessonite garnet. countries. Carved by Robert Jüchem, Idar-Oberstein, Germany.

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Ornamental variscite: A new gemstone resource from Western Australia discoloration. Some cut material has been Photo credits 1971–1979. Colchester Archaeological impregnated with cyanoacrylate, an acrylic Henri Oorjitham: 1a, 15a. Josep Bosch: Report 2 (Colchester Archaeological resin, to stabilize the interstitial materials 2a. Susan Stocklmayer: 1c, 2b, 3, 4, 7a, Trust Ltd), 34 and obviate damage. 7b, 8a. Margot Willing: 1b, 5a, 5b, 6b, 11a, Dana, E.S., 1892. The System of Mineralogy Reflectance spectra indicate that 11b, 15b, 16. Ian Robertson: 5c, 8c, 9a. of James Dwight Dana. 6th Edn. John the chromium Cr3+ ion is the main Ernest Nickel: 5d. Ian Pontifex: 7c, 7d, 8b, Wiley & Sons, Inc., 824 chromophore responsible for the attractive 9b. John Harris: V1, V4, V5, V6, 10. Dickerson, P., 1971. New notes from green colour of ‘Woodlands’ variscite. Utah’s treasure chest. Lapidary Journal, Early indications show that variscite can 25(6), 830-41 incorporate vanadium (V) in a number of Doelling, H. H., 1980. Geology and oxidation states. Reflectance spectroscopy References Mineral Resources of Box Elder County, may enable a quick assessment of V Alda, E., Bazán, B., Mesa, J.L., Pizarro, Utah. Utah Geological and Mineral oxidation state(s) and this may provide an J.L., Arriortua, M.I., and Rojo, T., 2003. Survey Bulletin, 115, 228-9 indicator of the conditions under which A new vanadium (III) fluorophosphate Dominguez–Bella, S., 2004. Variscite, a the formation of variscite occurred. X-ray with ferromagnetic interactions, prestige mineral in the Neolithic- (NH ) [V(PO )]. Journal of Solid State adsorption spectroscopy (XAS) studies of 4 4 Aeneolithic Europe. Raw material the ‘Woodlands’ variscite are currently part Chemistry, 173, 101-8 sources and possible distribution routes. of an investigation into the nature of and Arribas, A., Burg, J., and Nicolaou, J., Slovak Geol. Mag., 10(1-2), 147-52 the potential relationship between gold 1970. New occurrence of precious Forde, C.D., 1930. On the use of mineralization and the oxidation state of V variety of variscite in Spain. Lapidary greenstone (jadeite, callais, etc.) in in variscite. Journal, 24(5), 764 the Megalithic Culture of Brittany. The Balan, E., Allard, T., Morin, G., and Calas, Journal of the Royal Anthropological 3+ Acknowledgements G., 2002. Incorporation of Cr in Institute of Great Britain and Ireland, The authors wish to thank exploration dickite: a spectroscopic study. Physics 60 (Jan-June), 211-34 licence holders David Vaughan and Glenn and Chemistry of Minerals, 29, 273-9 Harrison, R.J., and Orozco Köhler, Archer, of Australian Outback Mining Bauer, M., 1904. Precious Stones. Charles T., 2001. Beyond characterization. Pty. Ltd., for the generous supply of Griffin and Company Ltd., London. 403 Polished stone exchange in the western gem-grade variscite used in this study; Calas, G., Galoisy, L., and Kiratisin, A., Mediterranean 5500-2000 BC. Oxford David Vaughan for the preparation of 2005. The origin of the green colour Journal of Archaeology, 20(2), 107-27 plane plates of variscite, and loan of of variscite. American Mineralogist, 90, Hooley, D., 1988. General points from carvings and cut specimens for testing 984-90 an accident of fortune. Archaeology in and photographing; Dr Michael Verrall Camprubi, A., Malgarejo, J.C., Proenza, York Interim, 13, 15-24 for collection of the XRD and SEM data J.A., Costa, F., Bosch, J., Estrada, Kniep, R., and Mootz, D., 1973. and assisting with data interpretation; A., Borell, F., Yushkin, N.P., and Metavariscite — A redetermination Dr E. Nickel, Research Fellow, CSIRO Andreichev, V.L., 2003. Mining and of its crystal structure. Acta. (ARRC), is acknowledged for verification geological knowledge during the Crystallographica, B29, 2292-4 of ‘Meßbach-type’, crystals of variscite and Neolithic: a geological study on the Larsen, E.S., 1942. The mineralogy and wardite, and assisting with the empirical variscite mines at Gavà, Catalonia. paragenesis of the variscite nodules formula; John Harris for digital capture of Episodes, 26(4), 295-301 from near Fairfield, Utah. Part 3, the visible spectrum©; Dr Ian Robertson, Cassen, S., 1998. Parameters of American Mineralogist, 27, 441-51 CSIRO (ARRC), for use of the camera for the neolithisation in the west of Laurs, B.M., Fritz, E.A., and Koivula, J. I., photomicroscopy; Josep Bosch, Curator France: From the circulation of 2007. Gems & Gemology, 43(1), 63-4 Neolithic Mines, Gavà, for loan of the prestige goods to the invention of Meireles, C., Ferreira, N., and de Lourdes image of the collar necklace; David symbols. 63rd Annual Meeting of Reis, M., 1987. Variscite occurrence Willing, for digital imaging; Francine the Society for American Archeology in Silurian Formations from Northern Payette for sourcing some references; Dr in the symposium: Prehistoric Portugal. Comun. Serv. Geol. Portugal, Vernon Stocklmayer for critiquing the communication: The first wheels, roads, 73(1/2), 21-7 manuscript. We would also like to thank metals, and monumental architecture Middleton, A., La Niece, S., Ambers, J., the Library staff at the CSIRO, Divisions of Clark, A.M., 1993. Hey’s Mineral Index: Hook, D., Hobbs, R., and Seddon, Floreat and Kensington (WA), and staff at Mineral Species, Varieties and G., 2007. An elusive stone: the use the Geological Survey, Library WA. Synonyms. Chapman and Hall and The of variscite as a semi-precious stone. Natural History Museum, London British Museum Technical Research Crummy, N., 1983. The Roman small Bulletin, 1, 29-34 finds from excavations in Colchester

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Ornamental variscite: A new gemstone resource from Western Australia

Muhling, P.C., and Brakel, A.T., 1985. Simpson, E.S., 1952. Minerals of Western Geology of the Bangemall Group- Australia Vol. 3. William H. Wyatt, the evolution of an intracratonic Perth, 690–5 Proterozoic basin. Western Australia Thomssen, R.W., 1991. Forgotten Geological Survey Bulletin, 128 phosphates of Fairﬁeld. Lapidary Neal, D. S., 1974. The excavation of the Journal, 45(4), 46-56 Roman Villa in Gadenbridge Park, Webster, R., 1975. Gems - Their Sources Hemel Hempstead 1963-1968. The Descriptions and Identiﬁcation, third Society of Antiquaries, London edn. Newnes-Butterworths, London, Nickel, E.H., Hancock, E., Thorne A., 322-3 Hough, R., Vaughan, D., and Verrall, M., 2008. Woodlands variscite — gold Websites occurrence in the North Gascoyne Hancock, E., 2008. Gold-Variscite region of WA (in press) mineralization in the Bangemall Novak, G.A., 1982. Verde web variscite Supergroup at Woodlands, Western from Lander County, Nevada. Lapidary Australia. http://www.wa.gsa.org.au/ Journal, 36(3), 544-52 WAG/WAG_Feb-Mar_2008.pdf (p.13) Querre, G., Herbault, F., and Calligaro, Mindat http://www.mindat.org/ Th., 2007. Long distance transport of Australian Outback Mining http://www. Neolithic variscite ornaments along the outbackmining.com/ European Atlantic arc demonstrated Dietrich, R.V., http://www.cst.cmich.edu/ by PIXE analysis. Proceedings of the users/dietr1rv/variscite.htm XI International Conference on PIXE and its Analytical Applications, Pueblo, Mexico, May 25-29, 1-5 Salvador-Salvador, P., and Fayos, J., 1972. Some aspects of the structural relationship between 'Messbach-type' and 'Lucin-type' variscites. American Mineralogist, 57, 36-44 Schindler, M., Hawthorne, F.C., and Baur, W. H., 2000. A crystal-chemical approach to the composition and occurrence of vanadium minerals. The Canadian Mineralogist, 38, 1443-56 Senior, B.R., and Chadderton, L.T., 2007. Natural gamma radioactivity and exploration for precious opal in Australia. The Australian Gemmologist, 23(4), 160-76

The Authors Margot Willing FGAA DipDT Perth, Western Australia. email: [email protected] Susan Stocklmayer FGA Perth, Western Australia. email: [email protected] Dr Martin Wells Perth, Western Australia. email: [email protected]

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Visually distinguishing A-jadeite from B-jadeite

Li Jianjun, Liu Xiaowei, Zhang Zhiguo, Luo Yueping, Cheng Youfa and Liu Huafeng

Abstract: Jadeite grades A and B are described in the context of the Chinese gem trade. Visual distinction of the grades is described, illustrated and discussed in terms of surface lustre, distribution of colour, nature of inclusions, internal reﬂ ection of light, microfractures and features of the fashioning of various items. Development of these recognition skills is recommended but recourse to the laboratory should always be an option for difﬁ cult items.

Keywords: China, gem grading, jadeite, treated gems, visual skills

Introduction Definitions of A-jadeite organic fi lling although it can be mildly The rapidly growing popularity of and B-jadeite destructive. collectables has caused increasing interest Jadeite carvers insist that a fi nal sealing in jadeite items, especially by ordinary The identifi cations of A-jadeite and of with wax is an essential completion Chinese citizens, and there is no reason B-jadeite can only be undertaken when step even for non-enhanced jadeite to believe the enthusiasm will diminish in the precise defi nitions of these materials items. However, it is not really practical the future. are understood. However, in China, there to attempt to distinguish between wax Determining the authenticity and is no formal description in any Chinese applied for polishing and that applied values of jadeite items can be diffi cult National Standard and the distinction for fi lling cavities and pores produced problems. Their valuation involves many between them is yet to be established, by acid treatment. This resulted in wax- contentious issues but one of the most especially for commercial use in this treatment for jadeites being listed as an important is differentiating between country. enhancement in the 1996 edition of the A-jadeite, the natural and non-improved It has been widely believed that Chinese National Standard (AQSIQ, 1996). jade, and B-jadeite which is the clarity A-jadeites have been only cut and In spite of this, it is currently widely enhanced version of natural jadeite. This polished without changing their accepted in the trade that such jadeite is especially important in commercial appearance or durability, while B-jadeites items treated with wax just for surface circumstances. have been acid treated and the developed glazing can still be classed as A-jadeite, The ordinary dealer or collector is cavities and pores have been fi lled with and therefore, the wax-fi lling does not not generally familiar with professional organic compounds (Fritsch et al., 1992). need to be disclosed in sale notes or gem identifi cation instruments, and the Organic compounds such as waxes, certifi cates. absence of detailed technical knowledge resins and epoxies can be diffi cult to Recently, it has been observed that about the production of B-jadeite, even identify when they have been applied as some jadeite items had been excessively amongst traders, means that evaluations sealants and fi llers. They are best detected treated with wax or other sealants to well made using basic instruments such as the and characterized using the infrared beyond that appropriate for fi nishing magnifi er may not be reliable. Being able spectrometer but this instrument was jadeite carvings. Gas bubbles are present to identify the different versions of jadeites not readily available in China until about in some of this material and can be seen simply by sight is, nevertheless, a highly 1996. Alternatively, a hot wire can be a with only the 10x loupe, sometimes even desirable skill. useful preliminary means of detecting without a lens. Consequently, the 2003

Visually distinguishing A-jadeite from B-jadeite edition of the Chinese National Standard contains numerous black inclusions of 2. distribution of coloration on the (AQSIQ, 2003) listed such impregnation various kinds. The material is sliced and surface with wax or sealant as the commercially- roughly formed. The thickness of the slices 3. nature of the internal inclusion defining treatment for B-jadeite. should not be significantly greater than that patterns Heat can also be used to turn some of the intended roughly formed items such 4. internal reflection of light resembling iron-pigmented jadeite red, and in the as bracelets, because the time required for the adularescence of moonstone Chinese National Standard this colour- the acid to penetrate and affect depths of 5. presence of micro-fractures changing heat-treatment is also considered more than about a centimetre is excessive, 6. size of the item and the quality and to be an enhancement (AQSIQ, 2003). which is unsatisfactory and expensive. The intricacy of the carving However, such thermally treated jadeite items are then treated with a solution of a Visually identifying jadeite as type still is considered to qualify as A-jadeite in strong mineral acid and controlled heating A or B requires careful and thorough a commercial sense. may also be beneficial to accelerate examination with attention to all of Therefore, the definition of A-jadeite the action. After sufficient time in acid these points in order to avoid erroneous which is accepted in the Chinese gem treatment the items are washed at least conclusions. trade is as follows. Type A-jadeite is twice in aqueous solutions of alkali to jadeite that has only been treated by neutralize any residual acid and are then Discussion of the key carving, polishing, or surface-filling with rinsed. A second treatment with a much points just a little wax to finalize the lustre weaker solution of acid is generally development; additionally, heating to conducted followed by a wash with a 1. Authenticating jadeites based on develop red colours and surface treatment weak alkali solution and a final rinse differences in surface reflectance or with a mildly-bleaching acid such as in water prior to drying in the open air. lustre oxalic acid or waxberry acid (but without Thus, the product is porous and chalky. When viewed under a suitable light damaging the structural integrity of the (If the operator wants to produce B+C source, larger polished items with stone) are also considered to still qualify jadeite, porous and chalky zones on the substantial curved or comparatively as A-jadeite (waxberry acid is derived items are selectively treated by hand with flat surfaces may provide detectable from the China waxmyrtle or China solutions of various dyes of appropriate differences in reflectance of A-jadeite bayberry of the family Myricaceae). colours which are readily absorbed to surfaces (Figure 1) compared with The accepted definition of B-jadeite is produce simulated patterning and colours those of B-jadeite. The more reflective as follows. Type B-jadeite includes jadeite resembling that of better quality untreated glazed surface with a brighter vitreous items which have been leached by strong natural jadeite.) Finally the items are dried gloss of A-jadeite contrasts with that of acid and the resulting pores and cavities and then submerged into a melted or the generally less-reflective polymer- then filled with sealant such as a polymer liquid sealant such as resin or uncured impregnated B-jadeite. (Fritsch et al., 1992) or with wax, the latter polymer and the air remaining in the pores Localized zones (or belts ) of surface of course being less durable or permanent and cavities in the jade is pumped out area may also show distinct variations than a thermoset polymer like an epoxy under vacuum. Releasing the vacuum then in the natures of the reflective highlights resin. allows the atmospheric pressure to force between A- and B-jadeites such that they C-jadeite is generally understood the sealant to impregnate the voids. If are really more a difference of brightness to mean dyed jadeite, but without necessary, the material is then cooled and than of colour. Imagining the view of the impregnation of sealant. This is not is ready for carving. jadeite to be just a black and white image discussed in this paper. can improve comparative assessments of Key points to be considered the relative intensities of these localized reflections. B-jadeite production in visually identifying A and In order to appreciate some of the more B-jadeite 2. Surface ‘colour levels’ subtle differences between A and B-jadeite, Some of the rather subjective factors If A-jadeites with high transparency the production process of B-jadeite which can be used to distinguish and an even texture are viewed with is outlined below. Starting material A-jadeite from B-jadeite are listed and strong light, (for example, direct sunlight), appropriate for treatment is selected. Its are then discussed in more detail below. the surface will appear to develop a ‘cold’ grain size and structure should be coarse Integration of these considerations can colour tone (Figure 2). This effect can also and conspicuous so that strong acid will then usually result in a moderately reliable occur on A-jadeites with an intrinsically easily attack and erode the undesirable assessment of whether the item can be ‘warm’ colour such as a yellow through components in the jadeite. Suitable categorized as A-jadeite or B-jadeite: brown to a red (see Figure 3). The material is generally of lower grade which 1. surface lustre or comparative appearance is probably a subjective enables a greater profit margin and it often reflectance differences mental evaluation of the sharpness of

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Visually distinguishing A-jadeite from B-jadeite

Figure 1: Example of vitreous refl ection which Figure 2: ‘Cold’ colour sharp refl ections on the is sharply defi ned and three light belts with surface of a green A-jadeite carving. sharp boundary on the back leg of the carving, characteristic of A-jadeite.

Figure 3: ‘Cold’ colour of well-defi ned refl ections also observed on the surface of A-jadeite with a Figure 4: Clear colour boundaries and unaltered Figure 5: An exquisite ‘qiao se’ effect, which yellow-brown ‘warm’ body tone compared to the green core zones in partially weathered jadeite, describes the use of different colour zones in ‘cool’ green of the jadeite in Figure 2. characteristic of A-jadeite. the A-jadeite to artistically demonstrate the uniqueness of the piece. the refl ected images rather than any real the surface of A-jadeite pieces, but these of a brown oxidized zone encapsulating difference in true colour perception, crisper ‘cold’ colour refl ections are less an unaltered green core is illustrated in analogous to the ‘hard’ and ‘cold’ crisp common on B-jadeite items with their Figure 4. brilliance of a well-faceted white diamond contents of sealants and fi llers. Modern technology is now quite compared to the more ‘soft’ and ‘gentle’ capable of imitating the brown component appearance of most of its less refractive 3. Inclusions that earlier was considered to be evidence simulants. This elevated level of ‘cold’ Natural inclusions in jadeites can of untreated A-jadeite so that its presence contrast generally appears only on the include brown or various alternatively is now less useful for differentiating A- surface of A-jadeite, presumably because coloured substances, black minerals and from B-jadeites. However, there may be the lower refraction of most of the organic ‘catkin’ pellets. The externally oxidized other evidence that can indicate A-jadeite sealants and impregnation agents used and differently coloured weathering shell rather then B-jadeite, such as a very fi ne for B-jadeite leads to its lower refl ectivity. surface of rough jadeites is a common quality of the carving technique, as well as Even most lay people who are usually epigenetic alteration, and its deliberate ‘qiao se’ (a feature indicating the skill in uninformed in the intricacies of jadeite retention in jadeite carvings to provide exploiting the irregular distribution of the treatments can appreciate this distinction aesthetic colour contrasts generally best natural colour to the best effect in the without diffi culty, so that when two indicates A-jadeite. However, false or available material as shown in Figure 5). different polished glossy objects without simulated ‘weathering shells’ may also be Black oxide inclusions mainly consist much difference in body colour, although encountered. Genuine weathering shells of chromite, magnetite or franklinite with distinct differences in refl ectivity are exhibit intense colour gradations and clear (a zinc, manganese and iron spinel), compared, impressions of different ‘colour boundaries between the oxidized zone apparent as opaque black dots and tones’ of ‘cold’ colour and ‘warm’ colour and the less affected interior. A genuine speckles. These black oxide particles are perceived. weathering shell gives the impression that commonly accompany the jadeite’s Sections of strong cold colour the oxidation colours have diffused from brilliant green, lavender or grey body refl ections which glisten with slight outside to inside, but a dyed imitation or colours which are developed by naturally movement of the light source or specimen false weathering shell gives a contrary incorporated transition metal ions such can be observed at different locations on impression. A genuine weathering shell as those of chromium, manganese and

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Visually distinguishing A-jadeite from B-jadeite

6 8 9

7 Figure 6: Reflective inclusion with metallic 10 lustre exposed at the jadeite surface; diagnostic evidence of A-jadeite. Figure 7: Black inclusion in a vivid green A-jadeite. Figure 8: Black inclusion within a mottled grey and green jadeite, indicating that it is probably A-jadeite. Figure 9: Greenish-blue epigenetic inclusion on a mesh-textured surface of an A-jadeite. Figure 10: A-jadeite with greenish-blue inclusion when observed in transmitted light. iron. Reflections produced by natural dark epigenetic inclusions that are absent in in Figures 11 and 12. They resemble inclusions with a metallic lustre such as dyed jadeite and, in terms of the Chinese the onset of flocculation in a solution, pyrite may indicate A-jadeite (see Figures jadeite trade, its appearance (as shown in and such features can also be present 6, 7 and 8), but one should also be aware Figures 9 and 10) is described as ‘coarse in B-jadeite; however, in much B-jadeite that small black particulate inclusions can ice dizi’ ( ‘dizi’ being a description applied polymer filling changes the appearance equally be found in the B (and C) grades by Chinese jadeite specialists to specify to tangled fibres or wisps as shown in of jadeite. Sometime the man-made black texture of jadeites), which indicates a Figure 13. spots in B- (and C-) jadeite will puzzle the texture like granular ice. Compared with dealer who thinks that they occur only in B-jadeite, A-jadeite can display orientation 4. Internal behaviour of light A-jadeite. of crystal growth, partially radiated resembling adularescence Surface characteristics caused by aggregates, and more often display longer The combination of reflection, greenish-blue secondary inclusions prismatic crystals (as shown in Figure 10). refraction, scatter, interference and (similar to dyed jadeite) in A-jadeite In A-jadeite with good ‘shui tou’ diffraction of light from many tiny (as shown in Figures 9 and 10) can be (transparency), there are commonly crystal faces and fissures in jadeite similar to those in B-jadeite. Typically isolated centres of white cotton-like fibres commonly creates an effect resembling in A-jadeite, one usually sees brown which are roughly spherical as shown adularescence, commonly yellow.

Figure 11: A-jadeite with roughly spherical Figure 12: Isolated round cotton-like inclusion in Figure 13: Blurry irregular cotton-like inclusions separate centres of white cotton-like inclusions. A-jadeite. in B-jadeite.

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Visually distinguishing A-jadeite from B-jadeite

Figure 16: A yellow glow is visible in the beads in Figure 17: The tiny ﬁ ssures in this A-jadeite the upper part of the A-jadeite carving. create an appearance like broken ice.

Figure 15a, which suggests that the Figure 14: A-jadeite with good ‘shui tou’ showing surface is very smooth, in contrast to that yellow internal refl ection. of the piece shown in Figure 15b which A-jadeite has a distinctly ‘cold’ surface has poor lustre and probably a coarse lustre but a ‘warm’ glow from internal surface microstructure. refl ected light, while B-jadeite does not This internal refl ection resembling have these features. Even on a blue adularescence is a signifi cant identifi cation background an A-jadeite with good feature for A-jadeites because even in ‘shui tou’ (transparency) shows a warm some jadeites with poor transparency, refl ection from its interior in Figures 14, there can be small regions of nice 15 and 16. transparency and even texture which In Figure 15a the halo around the generate this phenomenon. Buddha’s head shows a yellow glow Such an effect is absent in B-jadeite Figure 18: A-jadeite carving with a concave hollow in which fi ssures and crystal faces appear typical of A-jadeite, while the B-jadeite as the polymer (whose refractive index like broken ice. in Figure 15b shows a white-blue tone is closer to jadeite than that of air in in the halo. This latter effect is due to micro-space) effectively reduces the odds the treatment with polymer and some of refl ection (on the crystal faces and fl uorescence. micro-fi ssures faces) and scatter (among It is worth noting the highly refl ective the micro-crystals) of the transmitted light. area on the surface of the Buddha in Additionally the polymer’s fl uorescence is often blue-white. So it shows white in B-jadeite (in Figure 15b).

5. Authenticating jadeites based on a b tiny fissures: In A-jadeite, especially jadeite with

poor ‘shui tou’, fi ssures between crystals Figure 19: A-jadeite with white ridges, mid-left of (probably stress-induced) can often be picture, resulting from light refl ected from linear seen (Figures 17, 18 and 19). In B-jadeite, fi ssures, characteristic of A-jadeite. the fi lling of the interior fi ssures with modern polymers makes them less light (soft glow or effect resembling apparent. adularescence) which is also characteristic Figure 15: Two Buddha carvings. The halo The jadeite ring in Figure 17 has a of A-jadeite. around the head in (a) exhibits a yellow glow texture resembling broken ice and, in In Figure 19, the colour of the fi ssures characteristic of A-jadeite, while the halo in (b) addition, in the upper part, when one on the left is whiter than the body colour exhibits a white-blue refl ection, characteristic of observes it in transmitted light, it appears of the jadeite; the white fi ssures are the B-jadeite. yellowish because of the scattered sign of A-jadeite. Towards the centre of

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Visually distinguishing A-jadeite from B-jadeite the picture, and below the black metallic B-jadeites may also develop fissures on the colour of the pixiu body or the green inclusion, is an array of fissures in a exposure to hot light, especially the lights grain (called the ‘colour root’ in China) sinuous zone which also indicates that in showcases. is blocked by a noticeable fissure just the jadeite is A-grade. In B-jadeite interior In the A-jadeite carving in Figure 20, under the ear. This effect would not show fissures are commonly difficult to see on the right of the picture, the ear of the in B-jadeite because the colour would and at the surface they appear as veins pixiu (a legendary animal which can bring not be blocked; the colour of the ‘colour like earthworm traces. However, ageing good luck) appears white. This is because root’ would diffuse through the fissures, a phenomenon which Chinese experts call ‘colour drifting’. 20 22 The ‘colour root’ and ‘colour drifting’ are thus important concepts in identifying A- and B-jadeite in China. There are two types of ‘colour root’, one with boundaries and one without. Disappearance of the colour of a jadeite at a big fissure indicates an A-grade stone, while the disappearance of colour where texture remains unchanged indicates B-jadeite. 23 ‘Colour drifting’ is dependent on 21 the texture and grain of the jadeite, and while common in B-grade stones, is not restricted to them. Imagine compacted snowballs on which a drop of ink is applied. The ink will migrate along grain boundaries and the whole mass will assume some colour. In the terms of the Chinese gem trade, ‘dizi (texture) eats colours’ and ‘colours glorify dizi’.

6. The factors of size and quality of carving Jadeite articles can be subjectively 24 divided on the basis of size into two main groups: those carvings more than 3 cm across (about the size of an egg) and the rings, pendants and other jewellery items less than 3 cm thick (Figures 21 and 22). 25 Pieces more than 3 cm across are usually not ﬁlled with polymer, but jadeite jewellery made from slices (such as bracelets, two-dimensional ornaments with thickness less than 2 cm) should be examined carefully. Most B-jadeite comes from sliced material. The degree of intricacy and skill of the carvings serves as more important evidence in identifying jadeites than Figure 20: One of the pixiu’s ears appears white because there is a ﬁssure immediately beneath it. their basic shape. For example, the large Figure 21: B-jadeite jade carving. beautifully carved brush pot shown in Figure 22: B- and C-jadeite jade bracelets and ring. Figure 23 has a diameter larger than 3 cm Figure 23: A-jadeite brush pot. Figure 24: A-jadeite seal. and is A-jadeite. Figure 25: This jadeite with a sharp ridge is probably A-jadeite.

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Visually distinguishing A-jadeite from B-jadeite

References

Fritsch, E., Wu, S.-T., Moses, T., McClure, S.F., and Moon, M., 1992. Identification of bleached and polymer- impregnated jadeite. Gems & Gemology, 28(3), 176-87 General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China (AQSIQ), 1996. National Standard of P.R. China: Gem-Nomenclature. (GB/T16552-1996). Figure 26: The points of these drop-shaped Standards Press of China: Beijing, 10 cabochons are a good indication of A-jadeite. General Administration of Quality Supervision, Inspection and Quarantine of B-jadeite artefacts cannot be produced the People’s Republic of China (AQSIQ), with very great intricacy of carving 2003. National Standard of P.R. China: because their filling and sealing with Gem-Nomenclature. (GB/T16552-2003), polymers necessarily reduces their Standards Press of China: Beijing, 10 hardness. This restricts the shapes of B-jadeites to geometries without very sharp edges or points (Figures 25 and 26). Conclusion Mastering the skills described above would be of great benefit to dealers and ordinary consumers and is entirely possible with practice. However, because the visual skills still leave a margin for error in detecting frauds and such treatments as coating, reconstructing and dyeing, they should be used mainly for reference and only with caution at a commercial level. In some cases, turning to professionals in trade laboratories is the only way to reach accurate conclusions or get precise results.

The Authors Li Jianjun ([email protected]), Liu Xiaowei, Cheng Youfa and Liu Huafeng National Gold & Diamond Testing Center of China (NGDTC), Jinan, P.R. China Zhang Zhiguo National Gem Testing Center of China (NGTC), Beijing, P.R. China Luo Yueping National Jewellery Quality Supervision and Inspection Center of China (NJQSIC), Beijing, P.R. China

Page 131 The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

Abstracts

Diamonds diamonds included in Hadean zircons may and J. NOUET. Mineralogical Magazine, suggest that deep continental material may 72(2), 2008, 617-26. have existed as early as 4.2 Ga ago. Elements de caracterisation des Atomic force microscopy (AFM) and M.O’D. transmission electron microscopy (TEM) diamants naturels et synthétiques were used to investigate the ﬁne structure colorés. The use of laser and X-ray scanning to of the calcite prisms from the pearl-oyster E. ERIC. Revue de gemmologie AFG, 162, create a model of the historic Koh-i- shell Pinctada margaritifera. The AFM 2007, 4-13. analysis shows that the prisms are made Summary with illustrations of natural Noor diamond. S.D. SUCHER D.P. CARRIERE of densely packed circular micro-domains and synthetic coloured diamonds. M.O’D. and . Gems & Gemology, 44(2), 2008, 124-41. (in the 0.1 μm range) surrounded by a dense cortex. The TEM images and Diamond integrated quantum For centuries, the Koh-i-Noor was one of the world’s largest diamonds. It was diffraction patterns allow the internal photonics. recut in 1852 to an oval of structure of the micro-domains to be A.D. GREENTREE, B.A. FAIRCHILD, F.M. HOSSAIN 105.60 ct. Using one of the two plaster described. Each of them is enriched in and S. PRAWER. Materials Today, 11(9), casts now in the Natural History Museum, Ca-carbonate. Hosted in distinct regions 2008, 22-31. London, the present authors have of each prism, some are fully amorphous, Survey of the uses of diamond in the captured the surface topology of the and some others fully crystallized as quantum computer industry. Particular original Koh-i-Noor through photography subunits of a large calcite single crystal. coverage is given to the operation of plus laser and X-ray scanning methods. At the border separating the two regions, colour centres in diamond. M.O’D. A crystallographic analysis of the micro-domains display a crystallized major facets determined the diamond’s core and an amorphous rim. Such a Explosive maar-diatreme volcanism in orientation within a ‘perfect’ diamond border probably marks out an arrested unconsolidated water-saturated sedi- crystal, which was used to refute the crystallization front having propagated ments and its relevance for diamondif- theory that this diamond had been through a previously bio-controlled erous pipes. cut from the Great Mogul. Computer architecture of the piling of amorphous V. LORENZ. Gemmologie. Z. Dt. Gemmol. modelling established the orientation of micro-domains. Compared to recent data Ges., 57(1/2), 2008, 41-60. 5 photographs, the recut diamond within the historic concerning the stepping mode of growth 1 diagram, 3 maps. version. All this information was then used of the calcite prisms and the resulting Three examples of maar-diatreme to create an accurate replica from cubic layered organization at the μm-scale, these volcanoes formed in soft sediment are zirconia, offering a good approximation results give unexpected views regarding discussed: one in the Saar-Nahe basin in of the brilliance and optics of the original the modalities of biocrystallization. R.A.H. southern Germany, one carboniferous stone. R.A.H. midland valley basin in Scotland and L’Ambre Dominicain. the middle proterozoic diamondiferous A.B. COSTA. Revue de gemmologie AFG, diatremes of the Halls Creek Mobile belt 162, 2007, 15-16. in East Kimberley, Western Australia. E.S. Short note on amber from the Gems and Minerals Dominican Republic. M.O’D. Formation of Archaean continental Crystallization of biogenic Ca-carbon- lithosphere and its diamonds: the root About mineral collection. (Part 1 of 5.) ate within organo-mineral micro-do- of the problem. R. CURRIER. The Mineralogical Record, D.G. PEARSON and N. WITTIG. Journal of the mains. Structure of the calcite prisms 39(4), 2008, 305-13. Geological Society, 165(5), 2008, 895-914. of the Pelecypod Pinctada margaritifera First part of a survey of the profession The paper examines the formation (Mollusca) at the submicron to nano- and hobby of mineral collecting with of diamonds in the early evolution of the metre ranges. particular relevance to the United States. Earth; it is suggested that the presence of A. BARONNET, J.P. CUIF, Y. DAUPHIN, B. FARRE M.O’D.

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Abstracts (continued)

Coloring of topaz by coating and dif- Jadeite is a polycrystalline gemstone, H. LEITHNER. The Mineralogical Record, fusion processes: an X-ray photoemis- the transparency of which is greatly 39(5), 2008, 355-67. sion study of what happens beneath influenced by grain size and homogeneity. Wine-yellow crystals of gem-quality the surface. The grain boundaries are opened by topaz have been mined from the H. GABASCH, F. KLAUSER, E. BERTEL and T. weathering of the jade blocks in the Ebenstock granite in the Vögtland area RAUCH. Gems & Gemology, 44(2), 2008, river. Transparency can be improved in Upper Saxony, Germany. It is possible 148-54. by cleaning with acid and filling of the that crystals from this area were used in Surface-treated topaz has become pores. In green jadeite there is sometimes many European-made items of jewellery. a viable alternative to topaz coloured an isomorphous replacement of Al by Figures from Goldschmidt, Atlas der by irradiation, but unlike irradiation Cr. A mixed crystal series from jadeite Kristalformen (1922) are reproduced. which affects the entire stone, coloration to kosmochlor produces colourless to M.O’D. by chemical modification is limited to green to black material with increasing the near-surface region. The treatment RI and SG values. A new standard for Coated tanzanite. jadeite definition is being introduced in techniques are well established, but less is S.F. MCCLURE and A.H. SHEN. Gems & Hong Kong, accepting small amounts of known about how the processes involved Gemology, 44(2), 2008, 142-7. kosmochlor and omphacite; however, the create the desired appearance. X-ray The examination of 23 tanzanites the values must not exceed SG over 3.4 photoemission spectroscopy, combined coated by an apparently new technique and RI over 1.688. Materials within this with sputter depth profiling, has allowed revealed that the smaller (4–5 mm) stones field are called Fei Cui jade in China. E.S. the characterization of two fundamentally could be identified as coated, based on different colouring mechanisms for a combination of the unusually intense chemically treated topaz: coloured Les granats andradites-demantoides colour and microscopic examination coatings and diffusion-induced coloration. d’Iran: zonage de couleur et inclusions. which revealed surface iridescence as well R.A.H. S. KARAMPELAS, E. GALLOU, E. FRITSCH and M. as wear of facet junctions (small areas DOUMAN. Revue de Gemmology AFC, 2007, where the coating had been abraded Les gisements de corindons gemmes 107, 14-20. away). Two larger (3+ ct) stones did de Madagascar. A recently-discovered deposit of not show iridescence or wear (unless demantoid garnet is described from Iran. G. GIULIANI, D. OHNENSTETTER, A. FETY, examined at high magnification), and A content of more than 0.7% up to 1.2% M. RAKOTONDRAZAFY, A.E. FALLICK and others. were thus much more difficult to identify. of chromium oxide is required to give the Revue de gemmologie AFC, 159, 2007, XRF and LA-ICP-MS analyses showed green colour. Inclusions of fibrous calcite 14-28. the presence of Co, Zn, Sn and Pd in the are reported and specimens show marked The geology and mineralogy of gem- coating. R.A.H. colour zoning. M.O’D. quality corundum locations in Madagascar are discussed. A bibliography and map are Le Nigeria. Source de pierres de cou- included. M.O’D. Gem News International. leur. B.M. LAURS. Gems & Gemology, 44(2), 2008, J-C. MICHELOU. Revue de Gemmology AFG, 164-90. Le peuple Thrace en Bulgarie et les 159, 2007, 30-41. Brief descriptions are given of a mines du Laurium. The gem-producing potential of GONTHIER. 2.41 ct cut diamond with a brownish- E. Revue de Gemmology AFG, Migeria is discussed with particular orange inclusion (possibly eclogitic 162, 2007, 17-22. reference to beryl and corundum mineral garnet), under the table showing a strong Notes on the ancient lead slags of deposits and their geology. Nigeria is resemblance to a bird in flight, and of Laurium, Greece, and the possible use of compared with other African countries. a colourless diamond showing strong the minerals found there by the people of M.O’D. phosphorescence. Also mentioned are Thrace, present-day Bulgaria. M.O’D. an orange-red labradorite from China, an orange beryl from India, a rare faceted Le retour de l’émeraude. Quelques variétes d’ambre animal et Cr-rich clinochlore from Turkey, an J-C. MICHELOU. Revue de Gemmology AFG, d’ambre vegétal. orange danburite from Tanzania, faceted 163, 2008, 4-6. E. GONTHIER. Revue de Gemmology AFG, lawsonite form Marin County, California, General survey of emerald and its 163, 2008, 11-17. and a green Cr/V-bearing paragonite provenance. M.O’D. Summary of ambers or amber-like from northern Pakistan. Faceted peridot substances of animal and vegetable origin. extracted from a pallasite and rubies and Lab Notes. M.O’D. sapphires from a new locality in eluvial T.M. MOSES and S.F. MCCLURE (Eds). Gems & soil at Winza in central Tanzania are Gemology, 44(2), 2008, 156-63. illustrated. R.A.H. Einige Gedanken zu Jadeit-Jade. Items noted include a gem-quality H. HÄNNI. Gemmologie. Z. Dt. Gemmol. fancy brown CVD synthetic diamond with Ges., 57(1/2), 2008, 5-12, 5 photographs, 1 The Königskrone topaz mine, Sch- traces of boron, crystals of a bluish-green graph, bibl. neckenstein, Saxony, Germany. plagioclase coloured by copper, and a

Page 133 The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

Abstracts (continued) blue cut sapphire with an unusually high between blue specimens from Brazil absorption spectrum shows broad bands content of light rare earth elements. and Mozambique as trace element at 740 nm and 930 nm as well as a band R.A.H. compositions can overlap. M.O’D. at 510 nm. E.S.

Der Zonarbau des Alexandrits von Characterization of emeralds from a La Mine de Williamson. . SCOLIE, M. PHILIPPE SIRAKIAN Novello Claims, Simbabwe. historical deposit: Byrud (Eidsvoll), S and D. . Revue M. OKRUSCH, H. BRÄTZ and U. SCHÜSSLER. Norway. de Gemmology AFC, 107, 2007, 21-5. B. RONDEAU, E. FRITSCH, J.-J. PEUCAT, F.S. History and updated geological survey Gemmologie. Z. Dt. Gemmol. Ges., 57(1/2), NORDRUM GROAT. of the Williamson diamond mine at 2008, 13-22. 3 photographs 1 graph, 2 and L. Gems & Gemology, Mwadui, Tanzania. M.O’D. tables. 44(2), 2008, 108-22. The optically visible zonation of an An emerald deposit, mainly in alexandrite twin from the Novello claim small pegmatites intruding alum shales, Bei den Demantoid – Väschern von was investigated by EMP and LA-ICP-MS at Byrud, southern Norway, yielded Poldnevaja im Ural. analysis. The colouring elements of this significant amounts of crystals and gem M. SEHRIG. Lapis, 33(11), 2008, 32-5. stone were chromium and iron-titanium; rough in the late nineteenth and early Illustrated description of a significant zinc, gallium, vanadium and scandium twentieth centures. Complex multiphase deposit of demantoid garnet in the Urals, were found, the quantity varying with inclusions in the emeralds consist of Russia. M.O’D. zonal distribution. E.S. water, gaseous methane, halite, sylvite, calcite and a sulphide assemblage Structural characterization and chemi- (pyrrhotite, galena and sphalerite); this cal composition of aragonite and vater- Rhodochrosit aus dem Blei/Zink-berg- sulphide assemblage makes the Byrud werk Wudong bei Liubao, Guangxi, emeralds easy to distinguish from those ite in freshwater cultured pearls. A.L. SOLDATI, D. E. JACOB, U. WEHRMEISTER China. from elsewhere. They also have a and W. HOFMEISTER. Mineralogical A. OTTENS. Lapis, 33(10), 2008, 53-6. characteristic chemical composition, being Rhodochrosite of ornmanetal quality coloured mostly by vanadium (up to 1 Magazine, 72(2), 2008, 579-92. is described from the Wudong lead/zinc Vaterite and aragonite polymorphs in wt % V2O3) and contain low Mg and Ma mine, Guangxi, China. M.O’D. (≤ 0.1 wt % oxide). EPMA and LA-ICP-MS freshwater cultured pearls from mussels results are given. The relative amounts of the genus Hyriopsis (Unionidae) of Fe, Mg, Cr, Rb and Cs appear to be were structurally and compositionally Nouvelles des travaux sur le beryllium diagnostic. IR absorption spectra show characterized by Raman spectroscopy, et les saphirs bleus. that they contain little water. R.A.H. micro computer tomography, high V. PARDIEU. Revue de Gemmology AFG, 163, resolution field emission SEM, and LA- 2008, 7-9. ICP-MS. The appearance of vaterite in Gruene Quartze – Farbursachen und Review of beryllium-treated pearls is related to the initial stages of blue sapphires with illustrations of Behandlung. biomineralization, but vaterite can not R. SCHULTZ-GUETTLER, U. HENN C.C. characteristic inclusions. M.O’D. and be a precursor to aragonite. Vaterite is MILISENDA. Gemmologie. Z. Dt. Gemmol. not related to a particular crystal habit Ges., 57(1/2), 2008, 61-72. 10 photographs, and therefore does not have a structural Les tourmalines cuprifères du Nigeria 4 graphs, bibl. functional in the pearls. Larger contents et du Mozambique. Recently larger amounts of green of elements typically bound to organic B. RONDEAU and A. DELAUNAY. Revue de faceted quartz have been observed in the molecules, such as P and S in vaterite, Gemmology AFC, 107, 2007, 8-13 trade. Most of these owe their colour to as well as larger total organic contents Paraíba-type bright blue tourmalines artificial irradiation. The original material in vaterite as opposed to aragonite in owing their colour to copper are reported is a colourless to light yellow quartz from conjunction with larger concentrations of from Nigeria and from Mozambique. Rio Grande do Sul in Brazil. In contrast Mn2+ and Mg2+, imply a stabilizing role of Divalent copper, the origin of the colour, to green prasolites obtained by heat organic macromolecules and X2+ ions for gives a broad absorption band at 690 nm. treating amethysts, the colour will fade in biological vaterite. Distribution coefficients Some green and purple tourmalines show strong sunlight or in temperatures above between aragonite and vaterite for a similar band. Some green specimens 150°C. The samples investigated showed provenance-independent elements, also show a strong absorption of the a broad band in the absorption spectrum such as Mn and Mg (0.27 and 0.04, blue to the ultra-violet and this has been with a max of 592–620 nm. Prasolites respectively) agree very well with those attributed to trivalent manganese. Heat have a broad absorption spectrum around observed in fish otoliths. R.A.H. treatment up to 600–700°C has no effect 720 nm. Separation of heat treated and on the green colour while dark blue irradiated specimens is also possible with stones lighten. Purple stones become light the Chelsea colour filter when illuminated Nucleated cultured pearls: what is blue or colourless. Locality information with incandescent light: prasolites appear there inside. can be gained from the composition of green, irradiated specimens red. Synthetic M. SUPERCHI, E. CASTAMAN, A. DONINI, E. trace elements. There may be confusion quartz has also appeared in the trade; the GAMBINI and A. MARZOLA. Gemmologie. Z.

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Abstracts (continued)

Dt. Gemmol. Ges., 57(1/2), 2008, 33-40. found between apatite crystallinity, CO2- 3 Synthetics and Simulants Illustrated in black-and-white and in and OH- contents, and burial time. The colour, bibl. loss of organic matter from the ancient Discussions about nucleated cultured ivory may be the main reason why it is Single-crystal polarised-light FTIR pearls are generally related to the easily dehydrated and readily friable after study of an historical synthetic water- nacre: surface, treatment and thickness. being unearthed. R.A.H. Productions using nuclei obtained from poor emerald. F. BELLATRECCIA, G. DELLA VENTURA, M. materials other than mother-of-pearl Rhodonit. PICCININI GRUBESSI. (established by classical rules) have and O. Neues Jahrbuch S. WEISS. Lapis, 33(11), 2008, 36. started and are on the market without any für Mineralogie — Abhandlungen, 185(1), Illustrated summary of gem- and specific declaration. This report publishes 2008, 11-16 ornamental-quality rhodonite with some the results of a diffraction (Laue) testing Re-examination of an emerald important sites included. M.O’D. system applied to nucleated cultured synthesized by Hautefeuille and Perry pearls, which allows the distinction (1888) using a flux method has shown between nuclei obtained from mother-of- Herbert P. Obodda. it to be very close to the stoichiometric pearl, from shells having crossed lamellar J.S. WHITE. The Mineralogical Record, composition and homogeneous except for a significant variation in Cr O content structure or from a composite artificial 39(4), 2008, 315-31. 2 3 material called 'bironite'. E.S. Gem-quality vayrynenite from Pakistan (1.45–2.59 ct %); trace amounts of Ti, is featured as one of the very many rare Mg, Fe, Zn, Na, K and F were also noted. It has a 9.2264, c 9.1904 Å. Despite the Infrared spectroscopic study of mod- gem-quality crystals which have passed through the hands of noted American synthetic conditions, FTIR spectra in the ern and ancient ivory from sites at OH-stretching region show the presence Jinsha and Sanxingdui, China. mineral and gem dealer Herb P. Obodda of weak but significant H2O vibrations. L. WANG , H. FAN, J. LIU, H. DAN, Q. YE whose illustrated biography is given. and The polarized FTIR spectra collected with D M.O’D. M. ENG. Mineralogical Magazine, 71(5), E c consist of a unique sharp and intense 2007, 509-18. band at 3463 cm-1, whereas the E c spectra New primary gem occurrences in Sri Ancient ivory, buried for several consist of two minor bands at 3643 and thousands of years at the Chengdu Jinsha Lanka. 3587 cm-1. These bands are assigned ZWAAN ZOYSA. and Guanghan Sanxingdui sites in China, J.C. and E.G. Gemmologie. Z. to the ν3 antisymmetric stretching and has been compared with modern ivory, Dt. Gemmol. Ges., 57(1/2), 2008, 23-32. 9 ν1 symmetric stretching modes of type using IR spectroscopy in the 4000–400 photographs, 2 maps, bibl. II water in the structural channels, cm-1 range. By combining these results Primary pegmatitic and metamorphic respectively. These water molecules are with XRF data, the authors determined gem deposits of commercial interest probably associated with Li impurities in the crystallinity and crystal chemistry of have recently been discovered in Sri the mineral due to the flux used for the the apatite component, as well as the Lanka. In the Opanayaka district about synthesis. Using the molar absorption structural characteristics of the ivories. The 25 km south of Ratnapura aquamarines coefficient of Libowitzky and Rossman ancient ivory consisted almost entirely of have been found in pegmatites. Small (see American Mineralogist, 82(11-12), hydroxyl-carbonate apatite. Compared to hexagonal light- to grey-blue corundum 1997, 1111-15), a water content of ~ 30 modern ivory, the PO3- and CO2- bands crystals, some with more rounded 4 3 ppm is derived for this emerald. R.A.H. were stronger, the νPO4 IR bands were outlines, were found in the eastern corner clearly greater, and an extra OH- band of the highlands at Wellawaya and at at 3569 cm-1 was observed. These results Kamburipitiya reddish-orange hessonite imply that there is a greater degree of was found, 5–10% of fine gem quality, crystallinity in the ancient apatite, and 20–30% medium quality. Properties were that there has been incorporation and found to be similar to those of gems 2- recrystallization of CO 3 in the apatite found in the rich alluvial deposits of Sri during burial. Positive correlations were Lanka. E.S.

Abstractors R.A. Howie – R.A.H. M. O'Donoghue – M.O'D. E. Stern – E.S.

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Book reviews

Fleischer’s Glossary of Mineral Derbyshire, England, will feature in a later facilities rather than thumbing through Species. issue. This would be worth waiting for. three volumes. M.E. BACK and J.A. MANDARINO, 2008. The M.O’D. As frequently stated or alluded to in Mineralogical Record, Tucson. pp xiv, 345. the book, the basic premise of the study Price on application. of microscopic features in gemstones The tenth edition of this most useful Photoatlas of Inclusions in Gemstones, is that similar processes will result in a and convenient classic quick reference Volume 3. range of similar features in gems of the book follows its predecessors in its E.J. GÜBELIN and J.I. KOIVULA, 2008. Opinio same species. So whether these processes alphabetical list of validated species Publishers, Basel, Switzerland. pp 672, are geological, treatments or synthesis, with reference to the most important illus. in colour. ISBN 3-03999-047-4 significant information is stored within the citation in English, primarily American €250.00. gems that aid in their identification and Mineralogist and Mineralogical Magazine. Rarely has a gemmology book been separation. Group membership is indicated where so eagerly awaited and this, the third Whilst Volume 1 was portrayed as appropriate and the groups themselves, volume in the series of inclusions in a voyage of discovery and exploration with their constituent species, are gemstones by Eduard Gübelin (deceased into the world of inclusions in natural described at the end of the main text. 2005) and John Koivula, is excellent and gemstones, their treatments, imitations In this section the descriptions of some exceeds expectations. and synthetics, this volume builds on groups are expanded: this is particularly Volume 1, published in 1986, soon the geological and process correlation useful where the amphiboles are became a standard reference in the field established in Volume 2. This is a major described and here some references are of gemmology but it was not until 2005 strength of Volume 3 where, within made to important studies. that the second volume, which provided individual species and varieties (including The list of journals from which data greater depth and scope, was published. their synthetic counterparts and simulants) have been obtained is impressive and The major commercial gemstones, not only are they brigaded into geological covers six pages; non-English works are diamond, ruby, sapphire and emerald, not settings but within that grouping arranged included. covered in volume two, are the mainstay by locality or, in the case of synthetics and To make up a reliable and quick of volume three. simulants, by manufacturing process. At trio of books for reference, Fleischer The book covers exactly what it says the beginning of each of these groupings should be joined by the five volumes of in the title and more. The 672 pages there is text that briefly, but succinctly, Anthony et al. Handbook of Mineralogy contain 1796 images and it is indeed a covers the topics that the images illustrate. (1990–2003) and the full-colour Bernard huge reference library of images and the At the end of the primary text that and Hyrsl Minerals and their Localities practising gemmologist would be all the prefaces each gem material there is a (2006). Gemmological laboratories and poorer for its absence. useful list of additional reading references. teaching establishments without at least The quality of production is excellent Helpful, informative and often expansive two of these three should not be attracting and the images are often of exceptional captions that include illumination and customers! M.O’D. beauty. Anyone who has attempted magnification data complement the photomicroscopy will feel humbled by the impressive photographs that beautifully outstanding quality of the images which illustrate the diagnostic features. The Fluorite der Welt. Afrika, Amerika, are a testament to the skill, knowledge authors also discuss and illustrate the very Asien, Europa. extraLapis No. 35. and patience of the authors. I could find latest discoveries of mineral and fluid 2008. Weise, Munich, Germany. pp 103, only one image that had been published inclusions in gems. illus. in colour. €17.80. previously (exsolved rutile in ruby from There is a very brief Introductory The highly desirable extraLapis series East Africa – Volume 1) but the difference Section that outlines the basic premise continues with a beautifully illustrated in captions indicates that this feature had of the role that inclusions play in the overview of some of the world’s most been re-evaluated. Thus the resource of identification of gemstones and their notable ornamental fluorite deposits. images is cumulative for all three volumes. treatments. It is to be hoped that other deposits, In this respect the user would benefit Section two, Inclusions in Major for example the Blue John location in from the production of a DVD with search Commercial Gems, takes up 457 pages

Page 136 The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

Book reviews (continued) and is the meat of Volume 3. It begins is confined to the pernickety such as Working with Gemstones. A Bench with inclusions in diamonds. The application of current mineralogical Jeweler’s Guide. opening text covering mineral inclusions, nomenclature (e.g. tantalite – (Mn) as A.A. SKURATOWICZ and J. NASH, 2008. MISA/ peridotitic inclusions, eclogitic inclusions, opposed to manganotantalite, and the ASM Press, Providence RI. pp 128. ISBN inclusions from the deep mantle, cloud use of names that no longer have IMA- 09713495-4-1. Price on application. formations, the age of natural diamonds, approved species status (e.g. biotite; Pleasantly illustrated in colour, the diamond treatment, synthetic diamonds which it is now recommended be used book aims to present the major gemstones and diamond substitutes, gives an insight for a series such as the biotite-phlogopite to the working jeweller, manufacturer into the range of images that follow. series). One very minor irritation could and designer with practical advice on The diamond part of the section is be the presentation of descriptions on mounting, heat resistance and a number followed by inclusions in corundum. one page that pertain to images on a of other features that will assist both the These are conveniently arranged so that subsequent page such that some pages wearer and the buyer. The photographs inclusions in rubies and sapphires from have no captions: this occurs but rarely. It are high quality and the book design analogous petrological and geological would be wrong to give criticism because attractive. M.O’D. settings can be compared. Thus, for of omissions for as the authors state this example, rubies from Luc Yen and Quy is not a gemmological text book or gem Phenomenal Gems. Chau – Vietnam, rubies from Mogok and identification manual. F. and C. WARD, 2008. Gem Book Mong Hsu – Myanmar (Burma), rubies In conclusion, these highly respected Publications, Malibu, California. pp 64. from the Ganesh Himal area – Nepal, authors have produced an exceptional ISBN-13 978-1-887651-12-7. £10.95. rubies from Azad and Hunza – Pakistan book drawing on decades of meticulous An especially attractive newcomer and rubies from Jagdalek – Afghanistan optical microscopic examination, research to the Fred Ward Gem Book series, this are presented sequentially as they are and highly specialized photomicrography. book describes gemstones exhibiting examples of rubies found in marbles. The greatest challenge facing the chatoyancy, asterism, play-of-colour, Inclusions indicative of treatment follow gemmologist is the need to recognize and iridescence and other optical features. those typically found in natural corundum. separate natural gems from synthetics As always, Fred Ward’s pictures are Treatments illustrated are diffusion, and untreated stones from those that unmatchable and the book is a must. heating, fillings, coating, and oiling and have been treated. In facing up to M.O’D. dying. The synthetic corundum inclusions this challenge this current work is an illustrate the processes of flame fusion invaluable asset given that the gemstone (Verneuil), Czochralski pulling, floating industry has increasingly grown to depend zone and flux growth. The latter is further on the interpretation of inclusions. subdivided in the text by manufacturer: Collectively the Photoatlas volumes Chatham, Kashan, Ramaura, Knischka and make an outstanding contribution to the Douros. Unspecified Russian hydrothermal field of gemmology. B. J. growth, and the images are annotated accordingly. The third part of this section covers Gems & Gemology in Review: Treated emeralds arranged according to their Diamonds. genetic types, followed by inclusions J.E. SHIGLEY, 2008. GIA, Carlsbad, indicative of treatment and lastly California. pp 301. ISBN: inclusions in synthetics. It is here that 978-0-87311-054-9. £49.50. the authors, looking to the future, give Chapters in this excellently-produced examples of repair through re-growth; an book are adapted from papers already aspect considered only theoretical where published in Gems & Gemology and like gem rubies and sapphires are concerned. other compilations in the series cover the The third and final section deals with latest findings in a single subject area. The Inclusions in Rare and Unusual Gems. review could hardly have come at a more Arranged alphabetically the gems are critical moment for the diamond trade and andalusite, apatite, axinite, benitoite, will certainly be widely distributed and calcite, cordierite, danburite, diopside, used. ekanite, enstatite, fluorite, glass, gypsum, The chart in the back pocket illustrates kornerupine, pezzottaite, sapphirine, the diagnostic features of filled diamonds scapolite, sillimanite, sinhalite, spodumene and most usefully includes features and taaffeite. Introductory text prefaces of unfilled diamonds which could be each of these. mistaken for fillings. Criticism, none of which will This book is not just recommended – materially affect the gemmological user, it is essential. M.O’D.

Page 137 Gem-A Bookshop

Photoatlas of Inclusions Famous Diamonds in Gemstones Volume 3 5th edition E.J. Gübelin and J.I. Koivula Ian Balfour £210.00 £50.00

Working with Gemstones. Phenomenal Gems Gems & Gemology A Bench Jeweler's Guide Fred and Charlotte Ward in Review: Arthur A. Skuratowicz and £10.95 Treated Diamonds Julie Nash Edited by J.E. Shigley £19.95 £49.50

Prices exclusive of postage and packing

To place an order or for further information contact:

The Gemmological Association of Great Britain 27 Greville Street, London EC1N 8TN, UK t: +44 (0)20 7404 3334 f: +44 (0)20 7404 8843 e: [email protected] The Journal of Gemmology / 2008 / Volume 31 / No. 3/4

Proceedings of the Gemmological Association of Great Britain and Notices

Educational Sponsorship

This year has been a resounding success for Gem-A, the members-only, such as a searchable archives for The effects of which have been felt globally by our students Journal of Gemmology. and members. As an educational charity, we are extremely Currently under development is a new short-term grateful to our sponsors and supporters, who have helped natural pearl course, leading to a certificate of completion, us achieve many of our goals for 2008. which will be taught in conjunction with the Dubai The 100 Club and the Educational Sponsorship initiatives Pearl Exchange. The course will first be taught in Dubai were established in 2008 to invite members and supporters in Autumn 2009, and is another step taken towards to donate a minimum of £1000 each, which would be increasing worldwide accessibility of our courses. used towards the expansion and updating of our courses Until we reach our target of 100 members for the 100 worldwide. Thanks to our sponsors, The Gemmological Club, the 100 Club initiative will continue. A plaque to Association of Great Britain has been able to create the commemorate those who have donated to the 100 Club new Foundation in Gemmology course notes which are will be placed in the lobby of the Gem-A headquarters. now in use, containing up-to-date information and a Educational Sponsorship is an on-going initiative, and new look. In addition, Gem-A has launched an online we encourage 100 Club members and others dedicated education resource centre for students which incorporates to the Association to help us raise funds for 2009. As we access to web-based assignments, a glossary of terms, enter the second century of gemmological education, past papers, student forums and a calendar of events. A our need for your help is still great. Next year we need member version of the site will be launched in 2009, so funds to help us create course notes for a new Diploma that members of Gem-A can also have access to online in Gemmology course, set to begin in September 2009, education resources. Our new Foundation in Gemmology as the follow-up to the new-style Foundation course. We Open Distance Learning course will provide students with are also looking to raise funds to purchase gem-testing a refractometer, twenty stones, a full gem testing kit, a equipment for our student teaching facilities, for research gem reference guide and includes practical tuition within and for future supervised access for members. Donations the UK. With all of these added benefits for our distance in the form of gem testing equipment are also highly students, we are looking towards expanding internationally appreciated, and we would be delighted to receive a through our Open Distance Learning (ODL) Programme. simple Raman, or a new UV/VIS spectrometer to have in- With the help of our sponsors, Gem-A has also house for teaching. launched a new website. With a clean look that is easy For further information on sponsorship, or to see the to navigate, prospective students are better able to find list of sponsors on the web, visit http://www.gem-a. course information, and members and the trade are more com/membership/sponsorship.aspx. If you would easily able to find out about news and upcoming events. like to become a member of the 100 Club or become A members’ area of the website will be launched in 2009, an Educational Sponsor for 2009, please email olga. which will include exciting new features accessible to [email protected].

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Gem-A Awards

Gem-A Examinations were held worldwide in June 2008. In the Examinations in Gemmology 243 candidates sat for the Diploma Examination of whom 116 qualified, including 19 with Merit. In the Foundation in Gemmology Examination, 252 candidates sat of whom 176 qualified. In the Gem Diamond Examination 103 candidates sat of whom 50 qualified, including five with Distinction and five with Merit. The Christie’s Prize for Gemmology for the best candidate of the year in the Diploma Examination who derives their main income from activities essentially connected with the jewellery trade was awarded to Antonia Ross of Fleet, Hampshire. The Anderson Bank Prize for the best non-trade candidate of the year in the Diploma in Gemmology examination was awarded to Elizabeth Rasche of London. A new prize, the Diploma Practical Prize for excellence in the Diploma Practical Examination, was awarded for the first time, sponsored this year by Gwyn Green. The Diploma Practical Prize was awarded to Antonia Underwood of London. In the Foundation Certificate in Gemmology examination, the Anderson Medal for the candidate who submitted the best set of answers which, in the opinion of the Examiners, were of sufficiently high standard, and the Hirsh Foundation Award for the best candidate of the year, were awarded to Dr Pauline Jamieson of Edinburgh. The Bruton Medal, awarded for the best set of theory answer papers of the year in the Gem Diamond Diploma examination, was awarded to Kundan Sarraf from Kathmandu, Nepal. In addition to the medal, the winner received a copy of Diamond Cuts in Historic Jewellery by H. Tillander (donated by John Greatwood) and a Type II Diamond Spotter (donated by the SSEF Swiss Gemmological Institute, Basel). The Deeks Diamond Prize for the best candidate of the year in The Gem Diamond Diploma examination, was awarded to Jacqueline Larsson of Amsterdam, The Netherlands. The Tully Medal was not awarded. The names of the successful candidates are listed below.

Gemmology Diploma Qualiﬁed Agu, Cecile, Le Cannet, France Qualiﬁed with Merit Andersson, Joel, Umeå, Sweden Agarwal, Kamal Kishore, Jaipur, Rajasthan, India Au Chui Yee, Ada, Cascades, Homantin, Hong Kong Bai Feng, Beijing, P.R. China Baethe, Vanessa, Saint-Maur-Des-Fossés, France Bigford, Julie Claire, Malvern Wells, Worcestershire Benson, Jillian Rose, Toronto, Ontario, Canada Gao Xiao Huan, Shanghai, P.R. China Bhatia, Esha, Gujarat, India Giertta, Maria, London Booth, Eveline Violet, Cheltenham, Gloucestershire Harker, Catherine Anne, Birmingham, West Midlands Brian, Jeremy, Marseille, France Huang Jinming, Guilin, Guangxi, P.R. China Cai Qing, Wuhan, Hubei, P.R. China Ji Qiusong, Guilin, Guangxi, P.R. China Carre, Stephanie, Armées, France Kui Nui, Reema, Yuen Long, Hong Kong Claydon, Louise, Morden, Surrey Lau Ho, Kowloon, Hong Kong Coppack, Flavia, London Lek Chin Kwang, Singapore Day, Helen Laura, Norwich, Norfolk Luo Han, Guangzhou, P.R. China Dionne, Jean-Sebastien, Ste-Catherine-Jacques-Cartier, Nwe, May Moe, Yangon, Myanmar Quebec, Canada Peng, Hsiang Chieh, Taipei, Taiwan, R.O. China Drai, Stephanie, Clamart, France Ross, Antonia, Fleet, Hampshire Dunn, Katherine Joanna, Toronto, Ontario, Canada Sharma, Anita, Haryana, India Fontaine, Josee, St-Basile-le-Grand, Quebec, Canada Shaw, Heather Catherine, Barnsley, South Yorkshire Foran, Amelia Luetta, Toronto, Ontario, Canada Skalwold, Elise Ann, Ithaca, New York, U.S.A. Freeman, Sarah, London Wu Dehe, Guangzhou, P.R. China Gilli, Claude, Les Pennes Mirabeau, France

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Goldman, Lucy, London Valley, Aurelie, Amberieu-en-Bugey, France Hamren, Elisabeth, Ostersund, Sweden Veenhoven, Taletta W., Amsterdam, The Netherlands Ho Siu Ming, Shaukiwan, Hong Kong Wang Fang, Wuhan, Hubei, P.R. China Hui Yuet Ming, Kowloon, Hong Kong Wang Hongmei, Guilin, Guangxi, P.R. China Jaugeat Blaise, Vanves, France Wang Hui, Guilin, Guangxi, P.R. China Kamoune Yannick, Ndemanga, Pierrefitte-sur-Seine, Wang Li Geng, Hubei, P.R. China France Wang Liling, Guangxi, P.R. China Keeffe, Veronica Cheryl, Oshawa, Ontario, Canada Wang Weny-I, Tainan City, Taiwan, R.O. China Kim, Ji Eun, Busan, Korea Wang Youran, Hubei, P.R. China Kyaw Thu Min, Yangon, Myanmar Watrelos, Celine, Paris, France Lapsiwala, Foram Pravin, Gujarat, India Win, Thein Thein, Cricklewood, London Larsson, Ylva, Vado, Sweden Win, San San, Singapore Lee Hing Fan, New Territories, Hong Kong Wong Ka Yee, New Territories, Hong Kong Li Ying, Wuhan, Hubei, P.R. China Woo Ka Yin, Kowloon Bay, Hong Kong Liang, Jie, Birmingham, West Midlands Wu, Dandan, Guangzhou, P.R. China Liang Feng, Wuhan, Hubei, P.R. China Yang Jing, Wuhan, Hubei, P.R. China Liu, Huijing, Shanghai, P.R. China Ye Ying, Singapore Liu Yang, Wuhan, Hubei, P.R. China Yu Xiaoyan, Beijing, P.R. China Mao Li Hui, Wuhan, Hubei, P.R. China Yu Xuan, Wuhan, Hubei, P.R. China Martins Molgard, Silvia, Colombo, Sri Lanka Yuang Hongqing, Wuhan, Hubei, P.R. China Meraly, Afsana, Antananarivo, Madagascar Zaleszczyk, Alicja, London Mo, Zhuangguo, London Zhang Jieqin, Guilin, Guangxi, P.R. China Ng Wai Hing, New Territories, Hong Kong Zhang Qian, Wuhan, Hubei, P.R. China Nicolson, Louise Alexandra Patricia, London Zhang Wukun, Wuhan, Hubei, P.R. China Noronha Muthu, Sunita Karen, Gujarat, India Zhao Bo, Wuhan, Hubei, P.R. China Pan Yang, Scarborough, Ontario, Canada Zhong Xiangtao, Guilin, Guangxi, P.R. China Pang Le, Wuhan, Hubei, P.R. China Zhu Ye, Shanghai, P.R. China Panicco, Fabio Michel, Antanavarivo, Madagascar Perochon, Cyrielle, Castel-le-Lez, France Piirto, Irmeli Anja Susanna, Espoo, Finland Foundation in Gemmology Prendergast, Lorna, Great Missenden, Buckinghamshire Qualified Pwint Phyu Win, Yangon, Myanmar Akmeemana, G.G.N., Kandy, Sri Lanka Pyrro, Riku Matti, Kirkkonummi, Finland Asakawa, Masako, Johetsu-City, Niigata, Japan Qi Geng, Scarborough, Ontario, Canada Ayabe, Hiroko, Nishinomiya City, Hyogo Pref., Japan Qu Peng Cheng, Wuhan, Hubei, P.R. China Bahadur, Seema, London Rafferty, Frank, Ambrieres-les-Vallees, France Bahri, Sebastien, Feucherolles, France Ranorosoa, Nadine Joelle, Antananarivo, Madagascar Beer, Jasmin, Birmingham, West Midlands Razanadimby, Lalanirina, Antananarivo, Madagascar Bezant, Laura, Chelmsford, Essex Rufus, Simon, London Boele, Georgette, Les Acacias, Switzerland Samaratunge, Punyadevi, Horana, Sri Lanka Bright, David, The Hague, The Netherlands Shah, Prachi Hirenbhai, Surat, India Brom, Jean-Baptiste, London Siriwardena, Henarath H. D. Ajith Lal, Raddolugama, Sri Brown, Claire E., Perth, Scotland Lanka Brutsch, Sonia, Lucinges, France So Lai Yin, Shau Kei Wan, Hong Kong Campbell-Jones, Amy V., Sheffield, South Yorkshire Soh Shi Hong, Johor Bahru, Johor, Malaysia Cao Juan, Shanghai, P.R. China Soumaré, Myriam, Paris, France Cao Weifeng, Guilin, Guangxi, P.R. China Spauwen, Timotheus A. P., Geleen, The Netherlands Cartier, Laurent E., Basel, Switzerland Spencer, Jason, Birmingham, West Midlands Chang Cheng, Taipei, Taiwan, R.O. China Tan Kiat Choo, June, Johor Bahru, Malaysia Chang Hsuan Ming, Taipei, Taiwan, R.O. China Teng, Ying, Shanghai, P.R. China Chatzipanagiotou, Ioannis Tzannis, Attiki, Greece Teng Yongqing, Guilin, Guangxi, P.R. China Chen Shaofeng, Guangzhou, P.R. China Valerio Sa', Helena, Mississauga, Ontario, Canada Chen Jing, Guangzhou, P.R. China

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Chen Wei, Guangzhou, P.R. China Landale, Natalie, Wormshill, Kent Cheng Wing Yan, New Territories, Hong Kong Lau Shuk Ping, New Territories, Hong Kong Cheung Mei Yee, Agnes, Repulse Bay, Hong Kong Lee Hae Jung, Daegu, Korea Cheung Sau Yee, New Territories, Hong Kong Lee Wai Yin, Kitty, New Territories, Hong Kong Chok Yee Quin, Selangor Darul Ehsan, Malaysia Lepage, Anick, Mont Saint Hilaire, Quebec, Canada Chou Mei-Lien, Taipei, Taiwan, R.O. China Li Ah-Yun, South Croydon, Surrey Cox, Rebecca Jane, York Li Wenhui, Guangzhou, P.R. China De Souza, Mary-Anne, Carshalton, Surrey Li Li Lin, Guilin, Guangxi, P.R. China Deng, Baosheng, Guangzhou, P.R. China Li Jiaxuan, Guilin, Guangxi, P.R. China Dimitrakopoulos, Charalabos, Athens, Greece Li Yi, Guilin, Guangxi, P.R. China Do Mi Sun, Daegu, Korea Liang Huan, Guilin, Guangxi, P.R. China Duboeuf, Olivier, Nancy, France Lilley, Heather Jane, Newcastle-under-Lyme, Eastwood, Layla, Gerrards Cross, Buckinghamshire Staffordshire Eronen, Evelina, Lannavaara, Sweden Lindquist, Mia Caroline, Solna, Sweden Falah, Jamal, Blacktown, New South Wales, Australia Liu, Xianfeng, Shanghai, P.R. China Fellows, Nicola, Birmingham, West Midlands Lo Wai Sze, Causeway Bay, Hong Kong Feng Xi, Guilin, Guangxi, P.R. China Lo Wai Yee Bibian, Tsing Yi, Hong Kong Fraissinet, Laurent, Antananarivo, Madagascar Loke Hui Ying, Singapore Fu Kangyu, Guilin, Guangxi, P.R. China Ma, March Yu, Birmingham, West Midlands Gang Seo Hui, Jeollanam-do, Korea Ma Pui Man, Kowloon, Hong Kong Gough, Hannah Jane, Telford, Shropshire Ma Xu, Guilin, Guangxi, P.R. China Grounds, Camilla Sara, London Ma Yan Ting, Tsim Sha Tsui, Hong Kong Guenin, Nathalie, Sainte Foy, Quebec, Canada Maccaferri, Arianna, London Guo Yunrong, Shanghai, P.R. China McKenna-Venne, Doreen, Laval, Quebec, Canada Guo Haifeng, Shanghai, P.R. China Maltais, Paege, West Ealing, London Guo Hao, Guilin, Guangxi, P.R. China Matsuk, Daria, Maida Vale, London Guo Yengli, Guilin, Guangxi, P.R. China Meraly Afsana, Antananarivo, Madagascar Guy, Tracy-Anne, London Micatkova, Michaela, London Hanson, Lindsay, London Mikkola, Samuli, Oulu, Finland Hayry, Tiia, Helsinki, Finland Ming Yan, Guilin, Guangxi, P.R. China Hell, Martine Svitlana, Lannavaara, Sweden Mithaiwala, Priyanka M., London Hiipakka, Janica Elisabet, Lappeenranta, Finland Mizukami, Yusuke, Saitama City, Saitama Pref., Japan Ho Ming Yan, Hong Kong Island Nandwani, Shailja, Gujarat, India Holland, Nancy, Fuquay-Varina, North Carolina, U.S.A. Naylor, Peter D., Birmingham, West Midlands Horler, Rebecca Anne, Tunbridge Wells, Kent Ng Yuk Yu, New Territories, Hong Kong Hovi, Maria, Hyvinkaa, Finland Ngan Yin Ying, Kowloon, Hong Kong Huang, Yuan, Shanghai, P.R. China Ngao Mei Wan, New Territories, Hong Kong Huby, Melanie, Liège, Belgium Nishikawa, Takamichi, Nomura Kusatsu City, Shiga Hyvatti, Jaakko, Helsinki, Finland Pref., Japan Iggstrom, Per-Hakan, Rosersberg, Sweden Nishimura, Fumiko, Kofu City, Japan Ikeda, Tomoka, Imari Coty, Saga Pref., Japan Oike, Akane, Tokyo, Japan Jang Ae Ji, Daegu, Korea Olofsson, Marcus, Gothenburg, Sweden Ji Kaijie, Shanghai, P.R. China Oncina, Christelle, Aix-en-Provence, France Kagia, Georgia, Nikea, Greece Ouchene, Linda, Paris, France Kamal, Mohamed Azhar Ilham, Colombo, Sri Lanka Oxberry, Hannah Clare, Kings Lynn, Norfolk Kamoune Yannick, Ndemanga, Pierreﬁtte-sur-Seine, Panicco, Fabio Michel, Antanavarivo, Madagascar France Parvela-Sade, Anu, Espoo, Finland Kim Chan Ju, Daejeon, Korea Perochon, Cyrielle, Sainte-Therese, Quebec, Canada Kim, Ji Eun, Busan, Korea Petit, Gregory, Moraugis, France Ko Yum Sum, Iris, Kowloon, Hong Kong Petropoulou, Alexia, Athens, Greece Lai Yuen Wan, Eva, Stanley, Hong Kong Petropoulou, Eleni, Nea Smyrni, Athens, Greece Lam Shun, Kowloon, Hong Kong Plant, Grace, Stone, Staffordshire

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Platis, George, Athens, Greece Valley, Aurelie, Montreal, Quebec, Canada Pulecio, Gabriel, Bogota, Colombia Wakita, Yoko, Osaka City, Osaka, Japan Pulver, Caroline M.L., Nairobi, Kenya Walvius, Peter, Nijmegen, The Netherlands Qi Ming, Guilin, Guangxi, P.R. China Wan Ho Shun, Tuen Mun, Hong Kong Qin Qing, Guilin, Guangxi, P.R. China Wang, Cong, Fulham, London Qureshi, Erum Ali, Thane, India Wang, Songfang, Kofu-City, Yamanashi Pref., Japan Rabetaliana, Andoniaina Harijaona, Antananarivo, Wang Junyi, Guilin, Guangxi, P.R. China Madagascar Wetherall, Alan, Hitchin, Hertfordshire Rajaffand, Guy, Pantin, France Wiguna, Aland, Bangkok, Thailand Rakotomalala, Cedric Anthony, Antananarivo, Wilkinson, Catherine E.P., Blockley, Gloucestershire Madagascar Williams, Richard Marcus Andrew, Porthcawl, Ribarevic, Ivanka, Montreal, Quebec, Canada Mid Glamorgan Sahni, Harcharan Singh, Stourbridge, West Midlands Williams, Laura, London Seo, Jung Yeon, Daegu, Korea Wingate, Simon James, Tiverton, Devon Share, Rebecca Louise, Kingswinford, West Midlands Wong Nga Yin, Chaiwan, Hong Kong Shen Huanqun, Shanghai, P.R. China Wong Siu Yin, New Territories, Hong Kong Sigihara, Toshiyuka, Osaka City, Osaka, Japan Wong Wai Lam, Anita, New Territories, Hong Kong Sim Tam Yuk, North Point, Hong Kong Wu Na, Guilin, Guangxi, P.R. China Sun Norton, Central, Hong Kong Yamaguchi, Nao, Shikonawate City, Osaka, Japan Sung, Sophia, Taipei, Taiwan, R.O. China Yan Yaying, Guilin, Guangxi, P.R. China Szvath, Gabriella, Laukaa, Finland Yeung On Na, Kowloon, Hong Kong Tang, Michelle, Shanghai, P.R. China Yeung Yick Sin, New Territories, Hong Kong Tay Kunming, Singapore Young, Chun Yin Stewart, North Point, Hong Kong Tian Mi, Guilin, Guangxi, P.R. China Yu Zhiwei, Shanghai, P.R. China Tissa, V.G. Samith Madhawa, Colombo, Sri Lanka Zarandi, Annabel, London Tosun, Rachel Megan, Bo'Ness, West Lothian, Scotland Zhang Xiaohu, Guilin, Guangxi, P.R. China Trolle, Natascha, Copenhagen, Denmark Zhao Chunji, Shanghai, P.R. China Ueda, Kenji, Abeno-ku, Osaka, Japan Zhou Mengji, Shanghai, P.R. China Vajanto, Leena Maaria, Helsinki, Finland

Gem Diamond Examinations Gem Diamond Diploma Craddock, Natalie, Bridport, Dorset Cui, Xianzhong, London Qualified with Distinction Cui Xue, Wuhan, Hubei, P.R. China Gill, Julia Mary, Dudley, West Midlands de Fere, Susannah, London Larsson, Jacqueline, Amsterdam, The Netherlands Dessypri, Eleni, Athens, Greece Sarraf, Kundan, Kathmandu, Nepal Ding, Hui, Surbiton, Surrey Wootton, Sophie Louise, London Ewington, Craig A., London Yung Wai Lam, Hung Hom, Hong Kong Fraser, Brenna Heather, Kingston-upon-Thames, Surrey Gallant, Victoria, London Qualified with Merit Hsien Pui Ling, Tsuen Wan, Hong Kong Henning, Sarah Alexandra, Edgbaston, West Midlands Humphreys, Stephen J., Beckenham, Kent Naylor, Peter D., Birmingham, West Midlands Iwamoto, Akiko, London Russell, Marie, Worcester Kettle, Georgina Elizabeth, Birmingham, West Midlands Tidd, Lauren Elizabeth, Churchdown, Gloucester Kirk, Kelly Hope, Birmingham, West Midlands Tsantoulas, Apostolos, Athens, Greece Lam Cheuk Hei, Kowloon, Hong Kong Qualified Lee Ching Wah, Shatin, Hong Kong Bracey, Anne Christine, Birmingham, West Midlands Lui Fong, New Territories, Hong Kong Chen Wenlong, Beijing, P.R. China Lung Mei Ting, May, Shatin, Hong Kong Chen Xi, Beijing, P.R. China Moroz, Magdalena, London Corser, Elizabeth, Wellington, Shropshire Noble, Frances, Wendover, Buckinghamshire

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Nordgren, Pia Yu, Vallingby, Sweden Vikatos, Ilias, Patras, Greece Rajbanshi, Niren Man, Kathmandu, Nepal Wan Bresson, Wuhan, Hubei, P.R. China Richardson-Jefferies, Phillipa, London Watson, Sarah Louise, Rowley Regis, West Midlands Russell-Stoneham, Alexandra, London Wong Yin Tak, Tony, Kowloon, Hong Kong Smith, Mark, Richmond, Surrey Wratten, Nicholas William, Notting Hill, London Smith, Laura Sian, Oxford Yang, Yiwei, London Tai, Caroline, Tseung Kwan O, Hong Kong Yau Cho Kwan, Chai Wan, Hong Kong Tsoi Mei Yu, New Territories, Hong Kong Yip Wing Man Kennis, Kowloon, Hong Kong Vaughan, Angela, Limerick, Ireland

Gem-A Events Gallery at the Victoria and Albert Museum. In addition two workshops were held, one on a new approach to the Gem-A Centenary Conference use of the refractometer with Darko Sturman and Duncan and Second European Gemmological Parker, and the second on precious metal clay with Symposium Helen O’Neill. The ﬁnal event was a Gem Discovery Club During the weekend of 25 and 26 October at the Hilton Specialist Evening when Antoinette Matlins demonstrated London Kensington Hotel Gem-A hosted the Second the value of small, simple gem testing tools (a report of European Gemmological Symposium in conjunction this Specialist Evening is given on page 147). with our centenary celebrations. The dynamic two-day A report of the Conference will be published in the conference covered both the history of gemmology and December 2008 issue of Gems & Jewellery. the jewellery trade, and new techniques that are relevant to today’s gemmologists. The speakers included Sandra Graduation Ceremony Brauns, Rui Galopim de Carvalho, Emmanuel Fritsch, Al On Monday 27 October the Graduation Ceremony and Gilbertson, Henry Hänni, Ulrich Henn, Alan Hodgkinson, Presentation of Awards was held at Goldsmiths’ Hall in the John Koivula, Michael Krzemnicki, Yvonne Markowitz, City of London. Professor Alan Collins, Chairman of the Jack Ogden, Duncan Parker and Brad Wilson. Gem-A Council, presided and Gem-A President Professor A programme of events arranged to coincide with the Andy Rankin presented the awards. Conference held on Monday 27 and Tuesday 28 October Michael O’Donoghue and Terry Davidson who had included the Graduation Ceremony at Goldsmiths’ Hall retired from the Council during the year, were presented (see below), a guided tour of the Crown Jewels at the with certiﬁcates honouring their contribution to the work Tower of London with David Thomas, and a private of the Association. viewing of the new William and Judith Bollinger Jewellery

Conference Sponsors and Supporters:

The Association is most grateful to the following for their support: Major Sponsors Marcus McCallum FGA, London Benjamin Zucker, Precious Stones Company, New York, U.S.A. Supporters Apsara, Tadworth, Surrey Bear Essentials, Stone Group Labs, Jefferson City, Missouri, U.S.A. Marcia Lanyon Ltd, London The Prize Winners at Goldsmiths' Hall (from left): Antonia Underwood Maggie Campbell Pedersen FGA, London (Diploma Practical Prize), Kundan Sarraf (the Bruton Medal), Elizabeth Rasche (Anderson Bank Prize), Jacqueline Larsson (the Deeks Diamond dg3 Diversified Global Graphics Group for sponsoring Prize), Dr Pauline Jamieson (the Anderson Medal and the Hirsh Foundation the folders and delegate badge Award) and Antonia Ross (The Christie’s Prize for Gemmology). Photo courtesy of Photoshot.

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We were particularly pleased to welcome a number Centenary Dinner Sponsors of Fellows and Diamond members who had graduated in Gem-A examinations in past years. To mark the The Association is most grateful to the following for celebration of One Hundred Years of Gemmological their support: Education, those who had been unable to be present at the Graduation Ceremony in the year in which they Major Sponsors qualified, were invited to attend the 2008 event for the Venue: The Goldsmiths’ Company, London formal presentation of their Diplomas. Champagne Reception: SSEF, Swiss Gemmological In his address Professor Rankin referred to the Institute, Basel, Switzerland international status of our examinations saying to the Table Gifts: Fellows & Sons Auctioneers & Valuers, graduates: “Your Gem-A qualifications are recognized Birmingham, West Midlands Candlelit Chandeliers: Hazlems Fenton, Chartered throughout the world as the gold standard in training Accountants, London and education of professional gemmologists for the gem Flowers: QVC, London and jewellery industry. This recognition is in part due to Stationery: dg3 Diversified Global Graphics long-standing traditions of excellence over 100 years, and Group, London, and Peter G. Read FGA DGA, in part due to the a hard work and commitment you have Bournemouth, Dorset put into achieving your awards. You can be justifiably Programme Sponsors proud of your achievements which are being celebrated Backes & Strauss, London here today .” Chatham Created Diamond, San Francisco, California, Professor Rankin finished by again congratulating the U.S.A. graduates on their achievement and wishing them every David Gann, London success for the future. Reed Exhibitions, London The ceremony was followed by a reception for Theo Fennell, London graduates and guests. Raffle Sponsors A report of the Graduation Ceremony will be published Christie’s, London in the December issue of Gems & Jewellery. Designs from Memory, Bromsgrove, Worcestershire John Greatwood FGA, Mitcham, Surrey Pearl evening at Christie’s The Hilton London Kensington, London On 29 September Christie’s King Street kindly hosted a Marcus McCallum FGA, London champagne reception and pearl evening for the benefit Organic Gems, London of Gem-A’s educational initiatives. Presentations included Zultanite Gems LLC, Fort Lauderdale, Florida, U.S.A. ‘Pearls: a perspective on size and value’ by David Warren, Head of the Jewellery Department at Christie’s Dubai, ‘Pearl Fishing in Scotland’ by Kenneth Scarratt, Director Benjamin FGA DGA, valuer and jewellery consultant with of Research at GIA (Thailand), and ‘The Romance and considerable experience of the gem and auction trade History of Pearls’ by Gem-A CEO Dr Jack Ogden. both in the UK and overseas. A report of the event was published in the October A report of the event was published in the August issue issue of Gems & Jewellery. of Gems & Jewellery.

Centenary Dinner Hong Kong Graduation and Awards Dinner A dinner was held on 3 July at Goldsmiths’ Hall in A special dinner and graduation ceremony was held the City of London to celebrate one hundred years of in Hong Kong on 16 September at the Royal Palace gemmological education. The evening commenced with Restaurant, Tsimshatsui, Kowloon, in celebration of One a champagne reception in the setting of the Goldsmiths’ Hundred Years of Gemmological Education. The event Company’s exhibition ‘Treasures of the English Church’ was organized in conjunction with Gem-A’s teaching followed by a livery-style dinner. Those attending centres in Hong Kong, the Asian Gemmological Institute included representatives of international gem laboratories and Laboratory Ltd (AGIL) and the Hong Kong Institute and institutes, and members of the British gem trade of Gemmology (HKIG). The guest speaker was Charles auction houses. After dinner a speech was given by John Chan, President of the Hong Kong Jewellery and Jade

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Manufacturers’ Association. Speeches were also given by Gem-A CEO Dr Jack Ogden, Prof. Mimi Ou Yang Chiu Mei of HKIG and Dominic W.K. Mok of AGIL. A report of the event was published in the October issue of Gems & Jewellery.

Hong Kong Graduation and Awards Dinner Sponsors and Supporters

Gem-A is indebted to the many sponsors, donors and volunteers listed below who made the event possible. Major Sponsor Feng Hsiu-Yun FGA DGA, Taiwan Earth Gemmological Inc. ATC, Taichung, Taiwan R.O. China Sponsors Dr Ellen Lau GG FGA, Hong Kong Gemmological Association of All Japan, Tokyo, Japan Dinner Supporters Rosamund Clayton FGA DGA, London Qiu Zhi-Li FGA, Zhongshan University ATC, Guangzhou, P.R. China Prof. Mimi Ou Yang Chiu Mei FGA, Hong Kong Institute of Gemmology, Hong Kong

Dinner Prize draws, Table Prizes and Guest of Honour Charles Chan, President of the Hong Kong Jewellery and special donations Jade Manufacturers’ Association, speaking at the Hong Kong Graduation Luk Fook Jewellery and Awards Dinner. Prof. Mimi Ou Yang Chiu Mei FGA Eddie Fan Nature’s Treasures: Minerals and Gems 3-D Gold On 7 December at the Flett Lecture Theatre, Natural Hong Kong Jewellery & Jade Manufacturers' Association History Museum, London SW7, a seminar was held Louis Lo FGA, Sunning Holdings Ltd which had been arranged jointly between Gem-A, The Mercury in X Mineralogical Society and The Russell Society. Johnson Li Short talks on a wide range of topics including AGIL, Asian Gemmological Institute and Laboratory diamonds, inclusions, ancient gems, agates, mineral Limited luminescence, environmental aspects and many more HKIG, Hong Kong Institute of Gemmology were enjoyed by an audience of nearly 100. GAHK, Gemmological Association of Hong Kong After lunch, there were displays and demonstrations on J. H. Berry & Company, Goldsmiths various aspects of gems and minerals. Jewellery News Asia China Gems Magazine Kim Robinson Members’ Meetings Sun Po Gold Jewellery Ltd Appellation Limited London Victoria Dispensary Lu Coral Annual General Meeting Wu Chao-Ming FGA DGA The Gem-A Annual General Meeting was held at the Charles & Colvard Ltd. National Liberal Club, Whitehall Place, London SW1, on Kafa Coffee 30 June. Professor Alan Collins chaired the meeting and Action Design and Production Ltd welcomed members. The Annual Report and Accounts Prof. Yan Weixuan FGA DGA were approved. Professor Andrew Rankin was elected President for the period 2008-2010. Michael O’Donoghue

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Proceedings of the Gemmological Association of Great Britain and Notices and Evelyne Stern retired from the Council in rotation and being eligible Evelyne Stern was re-elected to the Gifts and Donations to the Association Council. Michael O’Donoghue did not seek re-election. The Association is most grateful to the following Jim Collingwood and John Greatwood retired from the for their gifts and donations for research and teaching Members’ Audit Committee by rotation and being eligible purposes: John Greatwood was re-elected to the Committee. Jim Chao-Ming Wu FGA DGA, Taipei, R.O. China, for a Collingwood did not seek re-election. Hazlems Fenton selection of polished jadeite slabs and rough sapphire were re-appointed as auditors for the year. crystals The AGM was followed by a presentation by David John R. Fuhrbach FGA BSc GG, JONZ Fine Jewels, Warren, Jewellery Department head of Christie’s London Las Cruces, USA, for a collection of rough and cut, King Street and Dubai. He shared anecdotes and tales natural and synthetic stones from his exciting 30 years of experience working with the Keecha Narayanamurthy FGA, Ipoh Perak, Malaysia, firm. Having been based in London, Glasgow, Hong Kong for a selection of rough black tourmaline and white and other areas, he specializes in developing the jewellery topaz departments of different regions and had just completed C.W. Sellors Fine Jewellery, Ashbourne, Derbyshire, his third successful sale for Christie’s in Dubai. for a selection of cut gems Prof. Weixuan Yan FGA DGA, Beijing, P.R. China, for a collection of 100 pieces of animal carvings, books Gem Discovery Club Specialist Evenings and photos, in memory of Prof. Zhonghui Chen The Gem Discovery Club meets every Tuesday evening at the Gem-A London headquarters when members have The 100 Club (£1000) the opportunity to examine a wide variety of stones. Once Joerg Baudendistel, Obertshausen, Germany a month, a guest specialist speaker is invited to give a Helen L. Plumb FGA DGA, Aberdeen, Scotland presentation. On 13 May the guest speaker was Dennis Allen, whose presentation focused on synthetic moissanite. Well Laboratory-grown Diamonds: Information Guide for known in the industry, Dennis Allen was a founder of HPHT-grown and CVD-grown diamonds (2nd edition). Emagold UK and was appointed President of the group On 28 October the specialist speaker was Antoinette for three years. He was also Chairman of the BJA in the Matlins, a respected gemmologist and well-known author early 1990s. He is now an industry consultant, a role that and lecturer. Often seen on several television networks includes acting as technical director for a diamond sight offering important consumer information, Antoinette holder and an advisor for TPS for the jewellery section of devotes much of her work to education and consulting the International Spring Fair. In his presentation, Dennis within the trade. Antoinette has an unusual ability Allen gave a background to synthetic moissanite since its to translate complex material into relevant, practical, introduction ten years ago, and explained what moissanite and — most important — useful information, and she is and how it was discovered. He then focused on the conducts product knowledge training for some of the growth in self-purchasing and how this has repositioned most prestigious retailers and industry groups in the synthetic moissanite, concluding with the current position USA. Many gemmologists today overlook basic tools and on sales and growth in the UK and customer comments on techniques that can be important aids to gem identification the product. and treatment detection; Antoinette’s specialist evening On 9 July the guest speaker was Branko Deljanin, was a fresh and invigorating look at the simple side of Director, EGL Canada, who gave a presentation on the gemmology. Her hands-on presentation demonstrated Identification of Small, Colourless and Fancy Colour the value of small, simple tools and gave the audience a HPHT-grown and CVD-grown Diamonds. Branko new appreciation for their value in this high-tech world, discussed both standard and advanced gemmological whether checking for treatments, checking parcels for methods, including microscopy, UV, FTIR spectroscopy, ‘salting,’ or guarding against HPHT enhanced diamonds. At XRF chemistry and PL Imaging and also problems in the end of the evening, the speaker signed copies of her identification of small laboratory diamonds, diamond new book Gem Identification Made Easy (4th edn). screening and testing, grading, certification and the CIS Two Gem Discovery Club Specialist Evenings were Fluorescence system. At the beginning of the evening, held in November. On 4 November the guest speaker was the speaker signed copies of his new 85-page book Thomas Dailing. With nearly 50 professional designing

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Proceedings of the Gemmological Association of Great Britain and Notices awards, Thomas has become one of North America's North East Branch most recognized jewellery designers. Thomas Dailing At a Branch meeting held on Thursday 23 October at Designs are contemporary classics, delicately balanced the Ramada Jarvis Hotel, Wetherby, West Yorkshire, Gwyn with dramatic artistry and a strong sense of engineering. Green, a Gem-A examiner and tutor, gave a presentation His creations typically showcase concave faceted gems by and a practical session on the identification of colourless Richard Homer. By continually pioneering new techniques, gems in jewellery. Gwyn’s presentation and practical Thomas Dailing brings his unique vision to the jewellery session appealed not only to students and valuers but also world. Thomas’s presentation with images of his creations to the working jeweller. focused on his history and progression as a jewellery designer and on his interaction with the legendary gem North West Branch cutter Richard Homer. Meetings held at the YHA Liverpool International, off On 11 November was a meeting with challenges Wapping, Liverpool, included a practical evening on 19 designed to assess the skills necessary for any successful June when participants had the opportunity to examine a stone dealer. There were many tests, such as parcel variety of rubies (synthetic and treated), diamonds (glass paper folding, gemstone weight estimation and valuing infill, and laser treated) and sapphires (synthetics). On 18 parcels of stones and during the evening participants September Andrew Spicer of Bonhams of Chester gave a had the opportunity to try their hand at ‘being a dealer’ talk entitled ‘Fakes and Forgeries in the Silver Markets’. themselves. The gem dealer and guest speaker was Jason At the Branch Annual General Meeting held on 16 Williams of G.F. Williams, London. Jason is on the Board October James Riley was elected Chairman, Secretary of Trustees of Gem-A; in order to source the best stones and Treasurer. The AGM was followed by a talk by Jo for his stock Jason travels extensively, bargaining hard Jones, an archaeologist and expert witness, entitled ‘Gem and exercising strict quality control, resulting in a fantastic Archaeology’. range of coloured stones. Scottish Branch Midlands Branch Monthly meetings held at the British Geological Survey, The Branch held their annual summer luncheon party Edinburgh, included a presentation and practical session on 16 June at Barnt Green. On 26 September a monthly on 11 June on the identification of colourless stones meeting was held at the Earth Sciences Department, in jewellery by Gwyn Green, a Gem-A examiner and Birmingham University, Edgbaston, where Branch Vice tutor. On 17 September Andrew Ross, Principal Curator Chairman Doug Morgan talked on the early development of Invertebrate Palaeontology and Palaeobotany at the of gem cutting, the practical problems in dealing with National Museums Scotland, gave a presentation on various gem materials, modern equipment and methods his observations on amber stability and properties. Dr for carrying out complex gem cutting as an art form. Cigdem Lule spoke on 16 October on the reasons why it On 31 October, also at the Earth Sciences Department, is important to have an understanding of gemmology in Dr Sally Baggott, Curator at the Birmingham Assay office, the jewellery business, citing zultanite from Turkey as an gave an illustrated talk on Birmingham Silver and the example. Influence of Matthew Boulton. On 11 November jewellery appraiser and expert witness On 28 November John Benjamin, an independent Peter Buckie gave a talk entitled ‘The challenge of valuing jewellery valuer, historian and author, traced jewellery one of the world's largest diamonds: appraiser's dream or design from the grim iconography of 1700s memento mori nightmare?’; this highlighted a faceted diamond weighing to neo-classicism and the era of sentimental jewellery in over 200 carats, D-colour, internally flawless, with the 1800s. Topics included how diamonds and gems were excellent symmetry and polish; that he had recently been cut and set, pastes, cut steel, Berlin ironwork, romanticism asked to value. and much more. A joint meeting with the Scottish Mineral and Lapidary The Midlands Branch Anniversary Dinner and Centenary Club was held on 23 October at the Club’s headquarters in Conference were held on Saturday and Sunday, 29 and Maritime Lane, Edinburgh. The speaker was Brad Wilson, 30 November at Menzies Strathallan Hotel, Edgbaston. Vice President and Fellow of the Canadian Gemmological Speakers included Doug Garrod, Gwyn Green, Henry Association, who gave a presentation entitled ‘Coloured Hänni, Alan Jobbins, Shena Mason and Vanessa Paterson. gemstone discoveries in Canada’.

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South East Branch Membership On 14 June members had the opportunity to view a collection of African gems and minerals, which were Between 1 June and 30 November 2008 the Council beautifully presented in a small private museum near approved the election to members of the following: Sevenoaks, Kent. Most of the specimens had been collected at source by our host over many years during the Fellowship and Diamond Membership (FGA course of his work in Africa. DGA) On 22 October at the Queen Elizabeth Room, Portland Chiu Wai Yu Yuki, Sheung Shui, Hong Kong. 2005; 2006 Place, London W1, Marcus McCallum gave a presentation Lai Sau Han, Winnie, Hong Kong. 2008, 2006 entitled ‘An Informal Chat with a Travelling Gem Dealer’. Peers, Soﬁa, London. 2005, 2006 Marcus, a well known and respected gem dealer based in Hatton Garden, focused on how he got into the trade, Fellowship (FGA) how things have changed over the years and shared some Agu, Cecile, Le Cannet, France. 2008 interesting anecdotes. Participants had the opportunity Baethe, Vanessa, The Hague, The Netherlands. 2008 to examine a variety of unusual specimens Marcus had Bigford, Julie Claire, Malvern Wells, Worcestershire.2008 brought along. Booth, Eveline, Cheltenham, Gloucestershire.2008 On 19 November members of the Branch had the Chan Wing Kwok, Tai Po, Hong Kong. 2008 opportunity to visit the new William and Judith Bollinger Chien Lien-Chin, Taichung City, Taiwan, R.O. China. 2008 Jewellery Gallery at the Victoria and Albert Museum. De Alwis Dissanayake, M.D., Colombo, Sri Lanka. 2008 The visit included an introduction to the gallery, which Ding Hui, Surbiton, Surrey. 2008 displayed more than 3500 pieces telling the story of Driscoll, Brian John, New York, U.S.A. 2008 Dunn, Katherine Johanna, Toronto, Ontario, Canada. 2008 European Jewellery during the last 800 years, by members Ellis, Trevor Edward, Birmingham, West Midlands. 1985 of the curatorial team, Richard Edgcumbe, Jo Whalley and Hamrén, Elisabeth, Ostersund, Sweden. 2008 Clare Phillips. Hon Wai Ching, Kowloon, Hong Kong. 2008 Hsu Chia Jung, Taichung City, Taiwan, R.O. China. 2007 Hui Yuet Ming, Kowloon, Hong Kong. 2008 South West Branch Jensen, Annalisa, London. 2006 Branch members were challenged by Jason Williams Keeffe, Veronica Cheryl, Oshawa, Ontario, Canada. 2008 of G.F. Williams of London to ‘Beat the Dealer’ at a Kui Nui, Reema, Yuen Long, Hong Kong. 2008 meeting held at BRLSI Building, Queen Square, Bath, on Kyaw Swar Htun, Yangon, Myanmar. 2008 9 November. This was an afternoon designed to assess Lau Yuen Yee, Simmy, Kowloon, Hong Kong. 2008 the skills which are necessary for any successful stone Lin Chun Hsien, Taipei, Taiwan, R.O. China. 2007 dealer. Time is money to a stone dealer; the faster you Maclellan, Kiki, London. 2008 are the more stones you can buy, sort and ultimately Mak Bing Lan, New Territories, Hong Kong. 2008 sell. However, you must also be accurate. Tests included Martins Molgard, Silvia, Colombo, Sri Lanka. 2008 spotting the rogue CZ in a parcel of diamonds, quickly Mathur, Chetna, Indore, India. 2003 Ng Wai Hing, New Territories, Hong Kong. 2008 and accurately sorting a matching set of stones from a Nicolson, Louise Alexandra Patricia, London. 2008 parcel, parcel paper folding, gemstone weight estimation Overton, Thomas William, Carlsbad, California, U.S.A. 2008 and valuing parcels of stones. He is on the Council of Pan Yang, Scarborough, Ontario, Canada. 2008 Gem-A and regularly speaks at branch meetings and Partridge, Jennifer Anne, Cambridge. 2008 London’s Gem Club. In order to source the best stones for Piirto, Irmeli Anja Susanna, Espoo, Finland. 2008 his stock Jason travels extensively, bargaining hard and Pyrro, Riku Matti, Kirkkonummi, Finland. 2008 exercising strict quality control. This results in a fantastic Qi Geng, Scarborough, Ontario, Canada. 2008 range of coloured stones, from small jobbing stones Rufus, Simon, London. 2008 to exquisite neon Paraiba tourmaline, colour-changing Shaw, Heather Catherine, Barnsley, South Yorkshire. 2008 alexandrite and lush green tsavorite. During the afternoon, Sikkema, Ariane, Almelo, The Netherlands. 2008 participants had the opportunity to see a range of Jason’s Siriwardena, Henarath H.D. Ajith Lal, Raddolugama, Sri stones. Lanka. 2008 Skalwold, Elise Ann, Ithaca, New York, U.S.A. 2008

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Soh Shi Hong, Johor Bahru, Malaysia. 2008 Leavey, Hariet, Yelverton, Devon Soumaré, Myriam, Paris, France. 2008 Lepage, Anick, Mont St Hilaire, Quebec, Canada Spagnoletti Zeuli, Lavinia, London. 2007 Lomas, John Proctor, London Spauwen, Timotheus A. P., Geleen, The Netherlands. 2008 Mclachlan, David, Woking, Surrey Spencer, Jason, Birmingham, West Midlands. 2008 Michaelides, Emma, Enﬁeld, Middlesex Strafti, Kalliopi-Maria, Athens, Greece.2008 Miller, Terrie Lynn, Tenby, Dyfed, Wales Tan Kiat Choo, June, Johor Bahru, Malaysia. 2008 Murakami, Akiko, London Thomas, Caan, Chesham, Buckinghamshire. 1998 Naylor, Peter D., Birmingham, West Midlands Tsang Wai Ming, Causeway Bay, Hong Kong. 2008 Nazari, Yasin, London Valerio Sa', Helena, Mississauga, Ontario, Canada. 2008 Neslen, Lewis, London Vildiridis, Athanasios, Athens, Greece. 1989 Parvela-Säde, Anu, Espoo, Finland Wang Weny-I, Tainan City, Taiwan, R.O. China. 2008 Patel, Maulika, London Patel, Priti, Harrow, Middlesex Premchamd, Purushothaman, Billericay, Essex Diamond Membership (DGA) Ramasamy, Sonia Kala, Selangor, Malaysia de Fere, Susannah, London. 2008 Rowe Rawlence, Emily, London Ng Che Keung, New Territories, Hong Kong. 2008 Salah, Ismail Jama, London Nordgren, Pia Yu, Vallingby, Sweden. 2008 Samuh, Elizabeth, London Richardson-Jefferies, Phillipa, London. 2008 Seubert, Michael, Munich, Germany Russell-Stoneham, Alexandra, London. 2008 Sheikh, Adnan, Luton, Bedfordshire Smith, Mark, Richmond, Surrey. 2008 Stöt, Linda, Stockholm, Sweden Tai, Caroline, Tseung Kwan O, Hong Kong. 2008 Szymaniak, Peter Jerzy, Watford, Hertfordshire Vikatos, Ilias, Patras , Greece. 2008 Thum Fu-Tsing (Leon), Penang, Malaysia Wong Kin Ching, New Territories, Hong Kong. 2006 Ward, Neil, Reighton Gap, North Yorkshire Yau Cho Kwan, Chai Wan, Hong Kong. 2008 Waugh, Andrew Donald, Braintree, Essex Williams, Richard Marcus Andrew, Porthcawl, Mid Associate Membership Glamorgan, Wales Yambala, Benoit Odimula, London Agrawal, Preeti, Kathmandu, Nepal Young, Stephanie, Chalfont St. Peter, Buckinghamshire Alawathage Don, Rohana Priyantha, Avissawewella, Sri Lanka An, Ran, London Transfers Boele, Georgette, Les Acacias, Switzerland Fellowship to Fellowship and Diamond Cargill, Jan, Arbroath, Scotland membership (FGA DGA) Crossley, Ursula, Augsburg, Germany Bracey, Anne Christine, Birmingham, West Midlands. 2008 Daughters, Paul, London Corser, Elizabeth, Wellington, Shropshire. 2008 Eastwood, Layla, Gerrards Cross, Buckinghamshire Cui, Xianzhong, London. 2008 Ekai, Richard Titus, Bangkok, Thailand Ding, Hui, Surbiton, Surrey. 2008 Evans, Charles, London Rajbanshi, Niren Man, Kathmandu, Nepal, .2008 Evans, Daniel Raymond, Brisbane, Queensland, Australia Sarraf, Kundan, Kathmandu, Nepal.2008 Evans, Eibhlin Ide, Skelmersdale, Lancashire Wootton, Sophie Louise, London. 2008 Ferracuti, Letizia, London Fox, Karen, Waterloo, Ontario, Canada Diamond membership to Fellowship and Hammond, Ross, London Diamond membership (FGA DGA) Harding, Jan, London Harker, Catherine Anne, Birmingham, West Midlands. 2008 Häyry, Tiia Marjiut, Hinthaara/Porroo, Finland Ho Siu Ming, Shaukiwan, Hong Kong. 2008 Hell, Martine Svetlana, Stjørdal, Norway Lee Hing Fan, New Territories, Hong Kong. 2008 Huang, Shih-Jung, London Jeans, Jane E., Healesville, Victoria, Australia Associate membership to Fellowship (FGA) Johnstone, Isobel Phoebe, St Lucia, Queensland, Australia Coppack, Flavia, London. 2008 Khan, Irfan Younas, South Shields, Tyne and Wear Freeman, Sarah, London. 2008 Kovanovic, Milena, London Giertta, Maria, London. 2008 Lajtha, Jessica, Loxwood, East Sussex

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Mo, Zhuangguo, London. 2008 As Editor, Roger has worked tirelessly to keep The Journal Prendergast, Lorna, Great Missenden, Buckinghamshire. to its renowned high standards, working closely with 2008 an international editorial panel and Mary Burland, the Rafferty, Frank, Ambrieres-les-Vallees, France. 2008 production editor. Ross, Antonia, Fleet, Hampshire. 2008 His retirement comes at a time when The Journal Win, Thein Thein, Cricklewood, London. 2008 is about to move online as an adjunct to the printed Woo Ka Yin, Kowloon Bay, Hong Kong. 2008 version and this change will provide new challenges and opportunities for the next editor. Associate membership to Diamond membership The Council of the Gemmological Association are (DGA) extremely grateful to Roger for all his hard work and Moroz, Magdalena, London. 2008 dedication over the years, and take this opportunity to Naylor, Peter D., Birmingham, West Midlands. 2008 thank him and to wish him well for the future. Yang Yiwei, London. 2008

Subscriptions 2009 It has been arranged that membership subscriptions will Gem-A is seeking a new remain unchanged for 2009 at £72.50 for UK members, £80.00 for those in Europe and £85.00 for overseas. HONORARY EDITOR for The Journal of Gemmology

The Journal of Gemmology The Gem-A Board is seeking an Honorary Editor We are pleased to announce that as from 2009, The for The Journal of Gemmology, to work from Journal will go online. We will be using a state-of-the-art home with occasional meetings at Gem-A, interface for this, providing full search facilities. Access London. will be via our website and will require membership log- Responsibilities will include proactively soliciting in. The articles will be peer reviewed as now and will be suitable papers, managing peer review, copy placed online as soon as they are ready. editing, proof reading and working closely with All online Journal articles will have a detailed summary the production editor. in our magazine Gems & Jewellery, explaining the interest, Applicants, whose ﬁrst language will be English, relevance and importance of the article, the science, if should be current Fellows of the Association and necessary, and, of course, pointing to the online article possess: where the full text, charts, tables and so on will published. These summaries will be readable and interesting brief s a demonstrable high level of articles, not to be confused with the succinct abstracts that mineralogical and/or geological will continue to be provided online. knowledge and understanding All the Journal articles placed online in 2009 will be also s editing skills and editorial experience published in ‘hard copy’ as a single issue in similar format to the present Journal and sent to all paid-up Gem-A s a suitable computer, broadband internet members as part of their 2009 subscription. connection and a reasonable level of IT skills, including knowledge of Word and Adobe Acrobat. Editorship of the Journal The Editor will receive an honorarium and some As the advertisement on this page shows, Gem-A is expenses. seeking a new editor for The Journal. Dr Roger Harding is retiring as editor of after 15 years. Roger was Director For further information contact Dr Jack Ogden at of Gemmology for the Gemmological Association from [email protected]. 1990 to 2003 and became Editor of The Journal in 1994.

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Gem-A Events 2009

Wednesday 21 January SCOTTISH BRANCH An evening with gems with Alan Hodgkinson Venue: British Geological Survey, Edinburgh

Friday 30 January MIDLANDS BRANCH Annual General Meeting followed by the annual Bring and Buy and Team Quiz Venue: Earth Sciences Department, Birmingham University, Edgbaston Friday 27 February MIDLANDS BRANCH The Cheapside Hoard by James Gosling Venue: Earth Sciences Department, Birmingham University, Edgbaston

Sunday 15 March MIDLANDS BRANCH Practical Training Day: Identiﬁcation of Gemstones Mounted in Jewellery Venue: Barnt Green, Worcestershire

Wednesday 25 March SCOTTISH BRANCH Scottish Pearl Evening at Cairncross of Perth Friday 27 March MIDLANDS BRANCH An Exploration into the World of Pearls by Gwyn Green Venue: Earth Sciences Department, Birmingham University, Edgbaston Friday 24 April MIDLANDS BRANCH Cometh the Day, Cometh the Jewel by David Callaghan Venue: Earth Sciences Department, Birmingham University, Edgbaston Friday 1 to SCOTTISH BRANCH CONFERENCE Monday 4 May Venue: The Queen's Hotel, Perth (Further details given on page 90) Sunday 21 June MIDLANDS BRANCH Summer Luncheon Party

Saturday 17 and GEMA ANNUAL CONFERENCE Sunday 18 October Venue: Hilton London Kensington

Monday 19 October GEMA GRADUATION AND PRESENTATION OF AWARDS Venue: Goldsmiths' Hall, Foster Lane, London EC2

Contact details Gem-A Headquarters: Olga Gonzalez on 020 7404 3334 email [email protected] Midlands Branch: Paul Phillips on 02476 758940 email [email protected] North East Branch: Mark Houghton on 01904 639761 email [email protected] North West Branch: James Riley on 01565 734184 or 07931 744139 email [email protected] Scottish Branch: Catriona McInnes on 0131 667 2199 email [email protected] South East Branch: Veronica Wetten on 020 8577 9074 email [email protected] South West Branch: Richard Slater on 07810 097408 email [email protected]

For up-to-the minute information on Gem-A Events visit our website at www.gem-a.com

Page 152 The Journal of

Gemmology2008 / Volume 31 / Nos. 3/4

Contents

73 A fancy reddish brown diamond with 125 Visually distinguishing A-jadeite from new optical absorption features B-jadeite Taijin Lu, T. Odaki, K. Yasunaga and Li Jianjun, Liu Xiaowei, Zhang Zhiguo, H. Uesugi Luo Yueping, Cheng Youfa and Liu Huafeng 77 A place for CZ masters in diamond colour grading 132 Abstracts M. D. Cowing 136 Book Reviews 85 The geological context of gems in the Velasco Pegmatitic District, Argentina 139 Proceedings of The Gemmological F. Guillermo Sardi Association of Great Britain and Notices

91 Magnetic susceptibility, a better 152 Gem-A Events 2009 approach to deﬁ ning garnets D. B. Hoover, C. Williams, B. Williams and C. Mitchell

105 The refraction of light by garnet depends on both composition and structure D. K. Teertstra

111 Ornamental variscite: A new gemstone resource from Western Australia M. Willing, S. Stöcklmayer and M. Wells

Cover Picture: Variscite set in 18ct yellow gold, containing Australian champagne, cognac and colourless diamonds, suspended from a diamond bead strand. Variscite fashioned by Murray Thompson; jewellery designed and crafted by Thomas Meihofer, Stacey Illman and Kristian Fraurud. Photo by Jurgen Lunsmann. (See Ornamental variscite: a new gemstone resource from Western Australia, page 111.)

The Gemmological Association of Great Britain

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