DOCSLIB.ORG

Volume 21 / No. 8 / 1989

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Volume 21 / No. 8 / 1989 Volume 21 No. 8. October 1989 TheJournalof Gemmology 63 GEMMOLOGICAL ASSOCIATION OF GREAT BRITAIN OFFICERS AND COUNCIL President: *Sir Frank Claringbull, Ph.D., EInst.E, FGS Vice-President: R. K. Mitchell, FGA Chairman: *D. J. Callaghan, FGA Vice-Chairman: *N. W Deeks, FGA Honorary Treasurer: *N. B. Israel, FGA Members elected to Council: *A. J. Allnutt, M.Sc, J. W Harris, B.Sc, *J. B. Nelson, Ph.D., Ph.D., FGA M.Sc, Ph.D. FRMS, ElnstE, FGA C. R. Burch, B.Sc, J. A. W Hodgkinson, FGA W Nowak, CEng., FGS D. Inkersole, FGA ER.Ae.S., FGA *C. R. Cavey, FGA B. Jackson, FGA M. J. O'Donoghue, E J. E. Daly, B.Sc, *E. A. Jobbins, B.Sc, C.Eng., MA, FGS, FGA FGA FIMM, FGA R. J. Peace, FGA *A. E. Farn, FGA *G. H. Jones, B.Sc, Ph.D., *EG. Read, CEng., A. J. French, FGA FGA MIEE, MIERE, FGA G. Green, FGA D. G. Kent, FGA *K. Scarratt, FGA *R. R. Harding, B.Sc, D. M. Larcher, FGA E. Stern, FGA D.Phil, FGA A. D. Morgan, FIBF, FGA *C. H. Winter, FGA ^Members of the Executive Committee Branch Chairmen: Midlands Branch: J. Leek, FGA North-West Branch: R. Perrett, FGA Examiners: A. J. Allnutt, M.Sc, Ph.D., FGA D. G. Kent, FGA E. M. Bruton, FGA P Sadler, B.Sc, FGS, FGA A. E. Farn, FGA K. Scarratt, FGA R. R. Harding, B.Sc, D.Phil., FGA E. Stern, FGA E. A. Jobbins, B.Sc, C.Eng., FIMM, FGA M. Virkkunen, M.Phil., FGA G. H. Jones, B.Sc, Ph.D., FGA C.Woodward, B.Sc, FGA Editor: E. A. Jobbins, B.Sc, C.Eng., FIMM, FGA Editorial Assistant: Mary A. Burland Curator: C. R. Cavey, FGA Secretary: Jonathan P. Brown, FGA, Barrister Saint Dunstan's House, Carey Lane, London EC2V 8AB (By Goldsmith's Hall) Telephone: 01-726 4374 The Journal of Gemmology VOLUME 21 NUMBER EIGHT OCTOBER 1989 Cover Picture Irridescent glass with botryoidal form, exhibiting spectral colours due to interference on thin layers, f See 'Iridescent natural glass from Mexico', p.488. ) ISSN: 0022-1252 466 J. Gemm., 1989,21,8 F.G.A Three initials that could change your career The Gemmological recognised and respected Association of Great by companies and Britain has been actively organisations throughout involved in the very the gemmological world. beginning of Gemmology Indeed, each year many of as an independent them invest in the future by science. sponsoring their own Today, the Association candidates. takes pride in its The Gemmological international reputation as Association's course has a learned society been specially compiled into dedicated to the a series of teaching modules promotion of that are both readable and gemmological education lavishly illustrated. and the spread of Together they provide a gemmological knowledge. comprehensive step-by-step The Association's guide to the fascinating coveted Fellowship is a world of gemmology. And an mark of excellence only Gemrndk^icalAsscxiation opportunity to earn the bestowed upon individuals coveted initials FGA— who successfully undertake of Great Britain Fellow of the Gemmological the association's written Association of Great Britain. and practical examinations covering all aspects of To find out more complete the coupon below and gemmology as a science. we will immediately forward the Association's Not surprisingly, this prestigious diploma is prospectus giving full details of this unique course. Please complete and return to: Gemmological Association Training Scheme, Saint Dunstan's House, Carey Lane, London EC2V8AB. Tel: 01-7264374 n Name Position Company_ Address . Telephone. J. Gemm., 1989,21,8 467 Star sapphire from Kenya N. R. Barot*, A. Flamini**, G. Graziani*** and E.J. Gübelin**** *Ruby Centre (Kenya) Ltd, Fedha Tower, 2nd Floor, Miundi Mbingu St., PO Box 47928, Nairobi, Kenya **1st Teoria Struttura Elettronica CNR, Via Salaria km 29.500, PO Box 10, 00016 Monterotondo Stazione, Italy ***Dip. Scienze della Terra, Università degli Studi di Roma 'La Sapienza', P. le A. Moro 5, 00185 Roma, Italy ****Benzeholzstrasse 11, 6045 Meggen, Lucerne, Switzerland Abstract well-shaped crystals. In the sapphire lots there are Various cabochon-cut star sapphire samples from the some pieces of dark brown to black obsidian, North-West of Kenya were examined to determine all brown zircon and translucent to opaque dark green the inclusions which may contribute to cause the epidote. asterism effect. Optical observations, electron microprobe and X-ray diffraction analyses were carried out. The inclusions Location and geology recognized were: cloudy areas, acicular inclusions, Corundum appears in Kenya as patches in meta- 'silk', tube-like inclusions, transparent crystals, 'feathers' morphic rocks (gneisses) which are believed to and healed fractures. The acicular inclusions responsiblehav e been desilicated by a dunite (Parkinson, for the asterism are separated into micro-striae 1947). The same applies to the corundum of the and needle-like inclusions. nepheline-syenite dyke-like bodies in the valleys Genetic growth considerations of these star sapphires (Joubert, 1966). are deduced. Usually the crystals are of dirty-brown colour and sometimes fractured. Introduction In the North-Western region, corundum is The world's main sources of star sapphire, up to found in Tertiary volcanic olivine basalts or in this time, have been Burma and Sri Lanka. Kenya secondary deposits (Bridges, 1982). is now entering the list and becoming the third The actual, geologically important, deposit is country and indeed the first country in Africa to not identified. Sapphires are being picked up from produce and supply star sapphire. the large desert type sandy area in the North­ Kenya and Tanzania, in addition to the many western region of Kenya. This is in the Turkana unusual gemstones, have been known to produce district of the Northern Rift Valley Province, and corundum in all possible colours and qualities lies on the West side of Lake Turkana (formerly from numerous occurrences. However, none of the Lake Rudolph) (Figure 1). sources ever supplied rough which can produce This region is part of the Mozambique orogenic star stones in commercial quantity. belt extending southwards to Malagasy and Several years ago, a small lot of blue sapphires Mozambique and northwards through the Sudan appeared on the Kenyan gem market of which and Ethiopia (Bridges, 1982). some samples produced a star. However, the source The area is in the middle of the Y-shape of the was never made known and similar or larger lots fault systems, and stretches from the turn off the never appeared on the gem market. main Lodwar road to the Sudan. This is a second­ Now the source has been relocated, and sapphire ary road (dirt road) leading to the Ethiopian border rough has started appearing on the local market through Murangering and Lokitaung villages (see since mid 1987. Hence the rough is available in map). commercially acceptable quality and quantity. Sapphires are mined from the top soil of desert Some other rough with a fair amount of trans­ type plains (Quaternary sediments) caused by the parency can be faceted to produce nice blue to erosion and peneplanation of hills, namely bluish-green gems. Lower grade rough can be used Pelekesh (1794m) and Mornerith (1438m). The to produce cabochons (without a star) and even primary source of the star sapphires and their beads. original occurrence is yet to be investigated. Most of the rough samples are slightly worn However, areas from which sapphires are probably crystals with frosted surfaces and a very low collected are shown by the dashed area in the map percentage (1-5%) of either completely rounded or (Figure 1). © Copyright the Gemmological Association ISSN: 0022-1252 468 J. Gemm., 1989,21,8 gemmologist an ETHIOPIA metal disc wit gemstones o ETHIOPIA gemstone is illuminated for both the spectroscop ETHIOPIA ETHIOPIA ETHIOPIA ETHIOPIA ETHIOPIETHIOPIAA ETHIOPIA ETHIOPIA ETHIOPIA ETHIOPIETHIOPIAA ETHIOPIA ETHIOPIETHIOPIAA ETHIOPIA ETHIOPIA ETHIOPIA ETHIOPIA ETHIOPIETHIOPIA A ETHIOPIETHIOPIA A ETHIOPIA Fig. 1. This map shows the location of the star sapphires in the North-western region of Kenya. The mining area, dashed area in the map, is located in the Turkana district of the Northern Rift Valley Province on the west side of Lake Turkana. Rough sapphire: its grading and cutting star which displays six equally narrow rays, with The examined samples are in the form of ten characteristic angles intersecting at 60°; of equal cabochon-cut star sapphires (total weight: 1.253 length and brightness, extending fully in each gm). They cover various shades of body colour viz. specimen. A weak star not extending fully is blue, brownish-blue, greenish-blue, greenish- displayed by the cabochons nos. 3, 5, 6, and 8. yellow, and blackish-brown. This different behaviour is ascribable to devi­ They range in size from 3.6 x 3.8 x 1.7 mm to ations from the crystallographic arrangement of 5.9 x 5.3 x 3.0 mm; the weight of each specimen the elongated systems of inclusions in the body of was measured to be a minimum 0.060 to maximum the host sapphire, intergrown with the basal plane 0.782 gm. and aligned parallel to the prisms of first or second 'Silk' occurs in all the cabochons, but in eight of order. them it traverses the whole of the host sapphire and causes 6- and 12-rayed asterism. Nevertheless, Gemmological investigation in samples 9 and 10, the 'silk' appears densely The cabochon sapphires were subjected to woven, causing only 'silky-spots'. standard gemmological tests, and the results are The samples nos. 1, 2, 4, and 7 present a perfect discussed below. J. Gemm., 1989, 21,8 469 Visual appearance and absorption spectra segregated into five categories: The samples range in clarity and are classified as 1) Cloudy areas sapphires from medium transparent (diaphane) to 2) Acicular inclusions opaque.
Load more

Recommended publications
  • Pezzottaite from Ambatovita, Madagascar: a New Gem Mineral
    PEZZOTTAITE FROM AMBATOVITA, MADAGASCAR: A NEW GEM MINERAL Brendan M. Laurs, William B. (Skip) Simmons, George R. Rossman, Elizabeth P. Quinn, Shane F. McClure, Adi Peretti, Thomas Armbruster, Frank C. Hawthorne, Alexander U. Falster, Detlef Günther, Mark A. Cooper, and Bernard Grobéty Pezzottaite, ideally Cs(Be2Li)Al2Si6O18, is a new gem mineral that is the Cs,Li–rich member of the beryl group. It was discovered in November 2002 in a granitic pegmatite near Ambatovita in cen- tral Madagascar. Only a few dozen kilograms of gem rough were mined, and the deposit appears nearly exhausted. The limited number of transparent faceted stones and cat’s-eye cabochons that have been cut usually show a deep purplish pink color. Pezzottaite is distinguished from beryl by its higher refractive indices (typically no=1.615–1.619 and ne=1.607–1.610) and specific gravity values (typically 3.09–3.11). In addition, the new mineral’s infrared and Raman spectra, as well as its X-ray diffraction pattern, are distinctive, while the visible spectrum recorded with the spec- trophotometer is similar to that of morganite. The color is probably caused by radiation-induced color centers involving Mn3+. eginning with the 2003 Tucson gem shows, (Be3Sc2Si6O18; Armbruster et al., 1995), and stoppaniite cesium-rich “beryl” from Ambatovita, (Be3Fe2Si6O18; Ferraris et al., 1998; Della Ventura et Madagascar, created excitement among gem al., 2000). Pezzottaite, which is rhombohedral, is Bcollectors and connoisseurs due to its deep purplish not a Cs-rich beryl but rather a new mineral species pink color (figure 1) and the attractive chatoyancy that is closely related to beryl.
    [Show full text]
  • Phenomenal Gemstones Possess Striking Optical Effects, Making Them Truly a Sight for Sore Eyes
    THE PHENOMENAL PROPERTIES OF GEMS Phenomenal gemstones possess striking optical effects, making them truly a sight for sore eyes. Here is GIA’s guide to understanding what makes each phenomenon so uniquely brilliant. ASTERISM CROSSING BANDS OF REFLECTED LIGHT CREATE A SIX-RAYED STAR-LIKE APPEARANCE. ASTERISM OCCURS IN THE DOME OF A CABOCHON, AND CAN BE SEEN IN GEMS LIKE RUBIES AND SAPPHIRES. ADULARESCENCE THE SAME SCATTERING OF LIGHT THAT MAKES THE SKY BLUE CREATES A MILKY, BLUISH-WHITE GLOW, LIKE MOONLIGHT SHINING THROUGH A VEIL OF CLOUDS. MOONSTONE IS THE ONLY GEM THAT DISPLAYS IT. AVENTURESCENCE FOUND IN NATURAL GEMS LIKE SUNSTONE FELDSPAR AND AVENTURINE QUARTZ, IT DISPLAYS A GLITTERY EFFECT CAUSED BY LIGHT REFLECTING FROM SMALL, FLAT INCLUSIONS. CHATOYANCY OTHERWISE KNOWN AS THE “CAT’S EYE” EFFECT, BANDS OF LIGHT ARE CAUSED BY THE REFLECTION OF LIGHT FROM MANY PARALLEL, NEEDLE-LIKE INCLUSIONS INSIDE A CABOCHON. NOTABLE GEMS THAT DISPLAY CHATOYANCY INCLUDE CAT’S EYE TOURMALINE AND CAT’S EYE CHRYSOBERYL. IRIDESCENCE ALSO SEEN IN SOAP BUBBLES AND OIL SLICKS, IT’S A RAINBOW EFFECT THAT IS CREATED WHEN LIGHT IS BROKEN UP INTO DIFFERENT COLORS. LOOK FOR IT IN FIRE AGATE AND OPAL AMMONITE (KNOWN BY THE TRADE AS AMMOLITE). LABR ADORESCENCE A BROAD FLASH OF COLOR THAT APPEARS IN LABRADORITE FELDSPAR, IT’S CAUSED BY LIGHT INTERACTING WITH THIN LAYERS IN THE STONE, AND DISAPPEARS WHEN THE GEM IS MOVED. INSIDER’S TIP: THE MOST COMMON PHENOMENAL COLOR IN LABRADORITE IS BLUE. PLAY OF COLOR THE FLASHING RAINBOW-LIKE COLORS IN OPAL THAT FLASH AT YOU AS YOU TURN THE STONE OR MOVE AROUND IT.
    [Show full text]
  • SOME UNUSUAL SILLIMANITE CAT's-EYES by E
    NOTES AND NEW TECHNIQUES SOME UNUSUAL SILLIMANITE CAT'S-EYES By E. Giibelin, M, Weibel, and C. P. Woensdregt Brown-black sillimanite cat's-eyes from Sri Lanka thin-section study and the ion etching necessary present an unusually sharp band, which would make for subsequent electron diffraction. them extraordinary gems wereit not for therather un- This article summarizes the results of the elec- attractive body color of the stones. A study of six of tron microscope study of the inclusions causing these stones found that they contain 0.5 wt.% iron the chatoyancy, as well as the gemological charac- oxide. The principal inclusion mineral is ilmenite, teristics of this unusual material. which occurs in elongated, submicroscopically thin lamellae. Complex thicker lamellae consist of hercy- EXPERIMENTAL METHODS nite spinel grown together with a member of the pyroxene group. These thicker inclusions were not Chatoyancy, like asterism, is caused by the scat- foundin all of the specimens investigated. tering of light on numerous fibrous inclusions aligned in one or more directions in the host crys- tal; proper cutting en cabochon is required to re- veal the phenomenon. For good chatoyancy or asterism, the elongated inclusions must be thin sillimanite, also known as fibrolite, is a common compared to the wavelengths of light (Weibel, metamorphic mineral. Cuttable material is ex- 1985). Such minute crystal individuals are not ac- tremely rare but is found in the Mogok Stone Tract cessible to ordinary microscopy and X-ray analy- of Burma and in the Sri Lankan gem gravels, as sis. Even though the inclusions may show up in a transparent rounded crystals with a blue, violet- thin section viewed with a polarizing microscope, blue, or grayish green hue (Webster, 1983).
    [Show full text]
  • Autumn 07 Cover
    Winter Antiques & Fine Art Auction Wednesday 28, Thursday 29 £5 & Friday 30 November 2018 ewbank’s auction sale dates 2018/19 Viewing days/times vary, please contact the auctioneer for details December 2018 August Thursday 13th Toys & Models Wednesday 7th Antique & Collectors inc. Silver Thursday 13th Entertainment & Memorabilia Wednesday 21st Antique & Collectors inc. Silver Friday 14th Vintage Posters Wednesday 21st Garden Furniture & Statuary Wednesday 19th Antique & Collectors’ Thursday 22nd Militaria, Stamps, Books & Maps Wednesday 19th Fine Wines & Spirits September January Wednesday 11th Jewellery, Watches & Coins Wednesday 16th Antique & Collectors inc. Silver Thursday 12th Silver & Fine Art Thursday 17th Decorative Arts Friday 13th Antique Furniture & Clocks Thursday 17th Contemporary Art & Modern British Paintings October February Wednesday 2nd Antique & Collectors inc. Jewellery & Silver Thursday 007th Bond & Beyond Wednesday 2nd Toys & Models Wednesday 13th Antique & Collectors inc. Silver Thursday 3rd Entertainment & Memorabilia Thursday 14th Militaria, Stamps, Books & Maps Thursday 3rd Movie Props Wednesday 27th Toys & Models Friday 4th Vintage Posters Thursday 28th Entertainment & Memorabilia Thursday 24th Decorative Arts Thursday 28th Movie Props Thursday 24th Contemporary Art & Modern British Paintings March November Friday 1st Vintage Posters Wednesday 6th Antique & Collectors inc. Silver Wednesday 6th Antique & Collectors inc. Silver Thursday 7th Asian Art Wednesday 20th Jewellery, Watches & Coins Thursday 7th Vintage
    [Show full text]
  • Mineral Collecting Sites in North Carolina by W
    .'.' .., Mineral Collecting Sites in North Carolina By W. F. Wilson and B. J. McKenzie RUTILE GUMMITE IN GARNET RUBY CORUNDUM GOLD TORBERNITE GARNET IN MICA ANATASE RUTILE AJTUNITE AND TORBERNITE THULITE AND PYRITE MONAZITE EMERALD CUPRITE SMOKY QUARTZ ZIRCON TORBERNITE ~/ UBRAR'l USE ONLV ,~O NOT REMOVE. fROM LIBRARY N. C. GEOLOGICAL SUHVEY Information Circular 24 Mineral Collecting Sites in North Carolina By W. F. Wilson and B. J. McKenzie Raleigh 1978 Second Printing 1980. Additional copies of this publication may be obtained from: North CarOlina Department of Natural Resources and Community Development Geological Survey Section P. O. Box 27687 ~ Raleigh. N. C. 27611 1823 --~- GEOLOGICAL SURVEY SECTION The Geological Survey Section shall, by law"...make such exami­ nation, survey, and mapping of the geology, mineralogy, and topo­ graphy of the state, including their industrial and economic utilization as it may consider necessary." In carrying out its duties under this law, the section promotes the wise conservation and use of mineral resources by industry, commerce, agriculture, and other governmental agencies for the general welfare of the citizens of North Carolina. The Section conducts a number of basic and applied research projects in environmental resource planning, mineral resource explora­ tion, mineral statistics, and systematic geologic mapping. Services constitute a major portion ofthe Sections's activities and include identi­ fying rock and mineral samples submitted by the citizens of the state and providing consulting services and specially prepared reports to other agencies that require geological information. The Geological Survey Section publishes results of research in a series of Bulletins, Economic Papers, Information Circulars, Educa­ tional Series, Geologic Maps, and Special Publications.
    [Show full text]
  • Download This Article PDF Format
    RSC Advances View Article Online PAPER View Journal | View Issue Cause analysis of chatoyancy of sapphires from Shandong, China† Cite this: RSC Adv.,2019,9, 24420 Jiaqi Yu, Xuemei He* and Zhiyun Lu Chatoyancy, that is, the cat's eye effect, has attracted many scholars' attention as a special optical effect. However, there are very few studies on the cat's eye effect of sapphire. The gemological features and formation mechanism of the chatoyancy of sapphires obtained from Shandong, China, were investigated by gemological microscopy, polarizing microscopy, scanning electron microscopy, infrared spectroscopy, X-ray fluorescence spectroscopy, UV-Vis spectroscopy, and Raman spectroscopy. Parallel orientations of the fracture surfaces were observed; light reflected on them, and an bright light band was formed perpendicular to them. No solid inclusions were detected under polarized light, and no absorption peaks of the solid inclusions were measured by Raman spectroscopy. In contrast, needle inclusions resulted in chatoyancy in other gemstones; parallel fracture surfaces with fluid inclusions Received 13th May 2019 above cause chatoyancy in sapphires. In this study, the origin of the cat's eye effect of sapphire was Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Accepted 22nd July 2019 analyzed innovatively, and its phenomena were characterized concretely. In addition, this study provides DOI: 10.1039/c9ra03585k a novel strategy to explain the mechanism of chatoyancy in the field of gemology and will be helpful for rsc.li/rsc-advances sapphire classification and quality evaluation. 1. Introduction crystallize in the early alkaline basalt magma rich in Al and poor in Si at a great depth under high pressure.14 One of the most Chatoyancy, known as the cat's eye effect, is a special optical prominent features of the sapphires obtained from Shandong is effect referring to a bright band on the surface of gemstones the coexistence of primary and secondary ores; this area mainly This article is licensed under a caused by the reection of light.
    [Show full text]
  • New Minerals Approved Bythe Ima Commission on New
    NEW MINERALS APPROVED BY THE IMA COMMISSION ON NEW MINERALS AND MINERAL NAMES ALLABOGDANITE, (Fe,Ni)l Allabogdanite, a mineral dimorphous with barringerite, was discovered in the Onello iron meteorite (Ni-rich ataxite) found in 1997 in the alluvium of the Bol'shoy Dolguchan River, a tributary of the Onello River, Aldan River basin, South Yakutia (Republic of Sakha- Yakutia), Russia. The mineral occurs as light straw-yellow, with strong metallic luster, lamellar crystals up to 0.0 I x 0.1 x 0.4 rnrn, typically twinned, in plessite. Associated minerals are nickel phosphide, schreibersite, awaruite and graphite (Britvin e.a., 2002b). Name: in honour of Alia Nikolaevna BOG DAN OVA (1947-2004), Russian crys- tallographer, for her contribution to the study of new minerals; Geological Institute of Kola Science Center of Russian Academy of Sciences, Apatity. fMA No.: 2000-038. TS: PU 1/18632. ALLOCHALCOSELITE, Cu+Cu~+PbOZ(Se03)P5 Allochalcoselite was found in the fumarole products of the Second cinder cone, Northern Breakthrought of the Tolbachik Main Fracture Eruption (1975-1976), Tolbachik Volcano, Kamchatka, Russia. It occurs as transparent dark brown pris- matic crystals up to 0.1 mm long. Associated minerals are cotunnite, sofiite, ilin- skite, georgbokiite and burn site (Vergasova e.a., 2005). Name: for the chemical composition: presence of selenium and different oxidation states of copper, from the Greek aA.Ao~(different) and xaAxo~ (copper). fMA No.: 2004-025. TS: no reliable information. ALSAKHAROVITE-Zn, NaSrKZn(Ti,Nb)JSi401ZJz(0,OH)4·7HzO photo 1 Labuntsovite group Alsakharovite-Zn was discovered in the Pegmatite #45, Lepkhe-Nel'm MI.
    [Show full text]
  • Colored Gemstone Report
    COLORED GEMSTONE REPORT Absorption Spectra Country of Origin Gemstone Identification The absorption spectra are a reflection of the electromagnetic The country of origin is the presumed geographical source Gemstones are minerals, rocks, organic, or inorganic materials radiation absorbed by a colored gemstone over a visible range of a colored gemstone, discoverable only for particular stones with that are, typically, cut and polished for use in jewelry. There are of wavelengths (approximately 400-800 nanometers). They are unique identifying characteristics. dozens of types of gemstones — including diamonds, colored recorded on a graph that plots the transmittance against wavelengths. gemstones, and pearls — each with a unique set of physical Cut (Shape and Style) and optical properties. Carat Weight Cut describes the silhouette or form created by a colored gemstone’s contours and facets. Shapes vary from round to fancy cuts, such Identifying Characteristics A carat is a unit of metric measurement used for colored gemstones. as cushion, emerald, heart, marquise, oval, pear, princess, and Identifying characteristics (IC) are physical aspects of a colored One carat (ct.) equals 100 points, 200 milligrams, or 1/5 of a gram. triangle. And style includes variations of brilliant, step, mixed, gemstone that help to confirm its singularity or categorization. and cabochon cuts. Beautiful stones can be found in virtually These can range from inclusions (fingerprints, needles, etc.) to any shape or style. modifiers caused by treatments (crystals with halos, reduced Color silks, etc.). In addition, IC can refer to instrument-based Colored gemstones are distinguished by their hue (primary Fluorescence measurements such as refractive index, x-ray fluorescence, impression of color), or by a combination of hue, tone (lightness), infrared spectra, Raman spectra, or specific gravity.
    [Show full text]
  • Nomenclature of the Garnet Supergroup
    American Mineralogist, Volume 98, pages 785–811, 2013 IMA REPORT Nomenclature of the garnet supergroup EDWARD S. GREW,1,* ANDREW J. LOCOCK,2 STUART J. MILLS,3,† IRINA O. GALUSKINA,4 EVGENY V. GALUSKIN,4 AND ULF HÅLENIUS5 1School of Earth and Climate Sciences, University of Maine, Orono, Maine 04469, U.S.A. 2Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada 3Geosciences, Museum Victoria, GPO Box 666, Melbourne 3001, Victoria, Australia 4Faculty of Earth Sciences, Department of Geochemistry, Mineralogy and Petrography, University of Silesia, Będzińska 60, 41-200 Sosnowiec, Poland 5Swedish Museum of Natural History, Department of Mineralogy, P.O. Box 50 007, 104 05 Stockholm, Sweden ABSTRACT The garnet supergroup includes all minerals isostructural with garnet regardless of what elements occupy the four atomic sites, i.e., the supergroup includes several chemical classes. There are pres- ently 32 approved species, with an additional 5 possible species needing further study to be approved. The general formula for the garnet supergroup minerals is {X3}[Y2](Z3)ϕ12, where X, Y, and Z refer to dodecahedral, octahedral, and tetrahedral sites, respectively, and ϕ is O, OH, or F. Most garnets are cubic, space group Ia3d (no. 230), but two OH-bearing species (henritermierite and holtstamite) have tetragonal symmetry, space group, I41/acd (no. 142), and their X, Z, and ϕ sites are split into more symmetrically unique atomic positions. Total charge at the Z site and symmetry are criteria for distinguishing groups, whereas the dominant-constituent and dominant-valency rules are critical in identifying species. Twenty-nine species belong to one of five groups: the tetragonal henritermierite group and the isometric bitikleite, schorlomite, garnet, and berzeliite groups with a total charge at Z of 8 (silicate), 9 (oxide), 10 (silicate), 12 (silicate), and 15 (vanadate, arsenate), respectively.
    [Show full text]
  • INTERNATIONAL GEMMOLOGICAL CONFERENCE Nantes - France INTERNATIONAL GEMMOLOGICAL August 2019 CONFERENCE Nantes - France August 2019
    IGC 2019 - Nantes IGC 2019 INTERNATIONAL GEMMOLOGICAL CONFERENCE Nantes - France INTERNATIONAL GEMMOLOGICAL August 2019 CONFERENCE Nantes - France www.igc-gemmology.org August 2019 36th IGC 2019 – Nantes, France Introduction 36th International Gemmological Conference IGC August 2019 Nantes, France Dear colleagues of IGC, It is our great pleasure and pride to welcome you to the 36th International Gemmological Conference in Nantes, France. Nantes has progressively gained a reputation in the science of gemmology since Prof. Bernard Lasnier created the Diplôme d’Université de Gemmologie (DUG) in the early 1980s. Several DUGs or PhDs have since made a name for themselves in international gemmology. In addition, the town of Nantes has been on several occasions recognized as a very attractive, green town, with a high quality of life. This regional capital is also an important hub for the industry (e.g. agriculture, aeronautics), education and high-tech. It has only recently developed tourism even if has much to offer, with its historical downtown, the beginning of the Loire river estuary, and the ocean close by. The organizers of 36th International Gemmological Conference wish you a pleasant and rewarding conference Dr. Emmanuel Fritsch, Dr. Nathalie Barreau, Féodor Blumentritt MsC. The organizers of the 36th International Gemmological Conference in Nantes, France From left to right Dr. Emmanuel Fritsch, Dr. Nathalie Barreau, Féodor Blumentritt MsC. 3 36th IGC 2019 – Nantes, France Introduction Organization of the 36th International Gemmological Conference Organizing Committee Dr. Emmanuel Fritsch (University of Nantes) Dr. Nathalie Barreau (IMN-CNRS) Feodor Blumentritt Dr. Jayshree Panjikar (IGC Executive Secretary) IGC Executive Committee Excursions Sophie Joubert, Richou, Cholet Hervé Renoux, Richou, Cholet Guest Programme Sophie Joubert, Richou, Cholet Homepage Dr.
    [Show full text]
  • Tiger Eye Meaning Properties
    Tiger Eye Meaning Properties Exploitive and unworking Aaron asseverate: which Robb is proximo enough? Expressional Petr foretoken some mince and infibulate his thermions so tarnal! Barbed Leighton free-lance very yesterday while Dick remains difficile and infrahuman. Eye meaning by tiger eye irradiates gentle blue tiger eye meaning properties of this stone it works on crystals. Identify any unknown crystal with our crystal identifier tool! It can alleviate pain and dampens an overactive nervous system and overstimulation of the adrenal glands. Tiger's Eye Healing Properties The Lilly Pad Village. Eye is temporary in Africa, as it to infuse shrimp with confidence, people suffering from quite different bone problems were advised to lovely water with powdered minerals which contained calcium. Change also helpful negative vibes from all luck stone the eye properties and properties of the world market is unique layers of the light. Please wait until page is loading! It is a bright green surface, it comes together. The Tiger Eye having been used for centuries and a nearly any ancient cultures and civilizations. This uniquely mixed stone is used to balance the Solar Plexus and Root Chakras. Tiger eye tiger meaning properties in tiger eye meaning discover the earth with gemstones should the lower chakras are. Tiger eye protects the anyone who wears it, nails, biggest tsunami and more. Please go this trip me. These are causing the wearer from the forms of them less iron is tiger eye meaning properties of the world are energetically cleared on. Maroon forms of tigereye are each always dyed or heated to butt or review that shade.
    [Show full text]
  • Winter 1999 Gems & Gemology
    WINTER 1999 VOLUME 35 NO. 4 TABLE OF CONTENTS EDITORIAL 173 Gems & Gemology Turns 65 Richard T. Liddicoat and Alice S. Keller 174 LETTERS FEATURE ARTICLE 176 Classifying Emerald Clarity Enhancement at the GIA Gem Trade Laboratory Shane F. McClure, Thomas M. Moses, Maha Tannous, pg. 185 and John I. Koivula NOTES AND NEW TECHNIQUES 186 Clues to the Process Used by General Electric to Enhance the GE POL Diamonds Karl Schmetzer 192 Diopside Needles as Inclusions in Demantoid Garnet from Russia: A Raman Microspectrometric Study Michael S. Krzemnicki pg. 187 196 Garnets from Madagascar with a Color Change of Blue-Green to Purple Karl Schmetzer and Heinz-Jürgen Bernhardt REGULAR FEATURES 202 Gem Trade Lab Notes 208 Gem News 224 Book Reviews 226 Gemological Abstracts 235 Index pg. 193 ABOUT THE COVER: In response to concerns expressed by the trade over the degree of pg. 201 clarity enhancement in emeralds, GIA Gem Trade Laboratory researchers have devised a methodology to establish the size, number, and position of filled fissures in an emerald, in order to classify the apparent degree of clarity enhancement achieved. The lead article in this issue reports on this research and the resulting classification system. The 10.5 ct emerald crystal in this gold and platinum pendant is from Jos, Nigeria. The pendant was designed by Elena Villa, and manufactured by Hans Dieter Krieger; it is courtesy of Gebrüder Bank, Idar-Oberstein, Germany. Photo © Harold & Erica Van Pelt––Photographers, Los Angeles, California. Color separations for Gems & Gemology are by Pacific Color, Carlsbad, California. Printing is by Fry Communications, Inc., Mechanicsburg, Pennsylvania.
    [Show full text]