Volume 21 No. 6. April 1989 TheJourna l of Gemmology

GEMMOLOGICAL ASSOCIATION OF GREAT BRITAIN OFFICERS AND COUNCIL

President: *Sir Frank Claringbull, Ph.D., F.Inst.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, A. D. Morgan, FIBF, FGA Ph.D., FGA M.Sc.,Ph.D. *J. B. Nelson, Ph.D., *E. M. Bruton, FGA J. A. W Hodgkinson, FGA FRMS, ElnstE, FGA *C. R. Cavey, FGA D. Inkersole, FGA W Nowak, CEng., E J. E. Daly, B.Sc, B. Jackson, FGA F.R.Ae.S., FGA FGA *E. A. Jobbins, B.Sc, CEng., M. J. O'Donoghue, *A. E. Farn, FGA FIMM, FGA MA, FGS, FGA A. J. French, FGA *G. H.Jones, B.Sc, Ph.D., *E G. Read, C.Eng., G. Green, FGA FGA MIEE, MIERE, FGA *R. R. Harding, B.Sc, D. G. Kent, FGA *K. Scarratt, FGA D.Phil, FGA D. M. Larcher, FGA *C. H. Winter, FGA

^Members of the Executive Committee

Branch Chairmen: Midlands Branch: J. Leek, FGA North-West Branch: R. Perrett, FGA South Yorkshire & District Branch: G. A. Massie, FGA

Examiners: A. J. Allnutt, M.Sc, Ph.D., FGA D. G. Kent, FGA E. M. Bruton, FGA R 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 TheJournal of Gemmology

VOLUME 21 NUMBER SIX APRIL 1989

Cover Picture Hat ornament exhibiting the sumptuous principal stone, the Dresden Green, natural size. (See 'The Dresden Green', p.351.) Photograph by Robert Bosshart

ISSN: 0022-1252 338 J. Gemm., 1989,21,6 GEMDATA - UPDATE 1 A computer program for gem identification

Now available in an updated version, GEMDATA is compiled in QuickBASIC and will run directly from MS-DOS on any IBM PC-compatible computer. It is designed to help with both appraisal identifications and gemmological studies. A full report of the program was given in the Journal ofGemmology, 20, 7/8,467-73. Optional yearly update of GEMDATA will be available. GEMDATA is supplied on a 5VWnch double-sided, double-density disk, and contains the following two sections :- Geml. Gem Identification from a databank of over 220 gems Gem 2. Gem Comparisons (side-by-side display of the constants of selected gems). Tables of RI and SG values, Gem Calculations (SG, reflectivity, critical angle, Brewster angle and gem weight/diameter estimation) The GEMDATA package, complete with disk, operating notes and gem index, costs £84.00 (plus postage and VAT). To order your package please use the coupon given on p. 398.

Gemmological Association of Great Britain Saint Dunstan's House, Carey Lane, London EC2V 8AB Telephone: 01-726 4374 Fax: 01-726 4837 Cables: Geminst, London EC2 JJ.. Gemm.Gemm.,, 1989,21,61989,21,6 333399

NoteNotess fromfrom thethe LaboratoryLaboratory —- 14 14

Kenneth Scarratt, FGAFGA

TheThe GeGemm TestingTesting LaboratoryLaboratory ofof GreatGreat Britain,Britain, 2727 GrevilleGreville Street,Street, London,London, EC1ECINN 8SU8SU..

FoForr manymany yearyearss ththee LaboratorLaboratoryy knewknew thatthat atat mamayy possiblypossibly bbee observeobservedd eitheeitherr sideside ofof ththee blue/blue/ somesome stagestage iitt woulwouldd havhavee toto obtaiobtainn aann instrumentinstrument greegreenn bordeborderr (say(say 500nm)500nm) iinn somesome naturanaturall oror whicwhichh 'described'described'' ththee absorbancabsorbancee andand transmitt­transmitt- treatetreatedd browbrownn greegreenn oror yelloyelloww diamondsdiamonds.. TheseThese ancancee ofof 'light''light' inin a graphicgraphic formform.. WhilsWhilstt thethe twotwo lineliness areare reportedreported byby AndersoAndersonn ttoo bbee situatedsituated hand-heldhand-held spectroscopespectroscope hadhad,, anandd stilstilll doedoess serveserve usus aatt 504504 anandd 497nm497nm.. TheThe actuaactuall measuremenmeasurementt foforr thethe extremelyextremely welwelll inin ththee identificationidentification ooff manymany gemgem '504''504~, whichwhich iiss ththee zero-phonon*zero-phonon* linlinee ooff ththee H3H3 species,species, inin a laboratorylaboratory itit doedoess havehave ititss limitations.limitations. centrecentre,, isis 503.2nm,503.2nm, anandd thatthat ooff ththee '497~'497', whicwhichh iiss EveEvenn B.w.B. W Anderson,Anderson, thethe fatherfather ofof gemmologic­gemmologic- thethe zero-phonozero-phononn lineline ooff ththee H4H4 centrecentre,, iiss aatt 496nm.496nm. aall spectroscopyspectroscopy anandd a loverlover ooff ththee hand-heldhand-held AtAt first glancglancee thesthesee smallsmall errorserrors iinn measurementmeasurement spectroscope,spectroscope, inin explainingexplaining hihiss observationsobservations hahadd atat maymay seemseem unimportanunimportantt bubutt asas ththee 496n496nmm linlinee maymay timestimes ttoo resortresort ttoo somewhatsomewhat imaginativeimaginative descrip­descrip­ onlyonly rarelyrarely bbee observedobserved iinn a naturallynaturally colouredcoloured tiontionss forfor somsomee characteristicharacteristicc spectra,spectra, e.g.e.g. ththee 'organ'organ diamonddiamond andand farfar mormoree oftenoften observedobserved iinn anan artifi­artifi­ pipe'pipe' spectrumspectrum seenseen iinn spinels.spinels. ciallycially irradiatedirradiated andand subsequentlysubsequently annealedannealed dia­dia­ ObservationsObservations witwithh ththee hanhandd spectroscopespectroscope apartapart mondmond,, ththee advantagesadvantages ofof havinghaving aann abilitabilityy toto bebe fromfrom fine lines,lines, iinn general,general, havhavee toto bbee describedescribedd inin absolutelabsolutelyy suresure abouaboutt youryour observationsobservations iiss obvious.obvious. vaguvaguee termtermss suchsuch asas,, 'a'ann areareaa ofof absorptioabsorptionn centredcentred ThisThis becomebecomess mosmostt apparenapparentt whewhenn oneone realisesrealises atat approximatelyapproximately...... ' ' andand thesethese araree mormoree thanthan suffi­suffi­ thatthat jusjustt toto ththee shortshort wavwavee sideside ooff ththee '496''496' iiss whatwhat ciencientt iinn thethe identificatioidentificationn ofof mostmost gegemm speciesspecies suchsuch cancan atat timetimess bbee a relativelyrelatively strongstrong absorptioabsorptionn lineline aass sapphire,sapphire, almandinealmandine garnet,garnet, peridotperidot,, diamond,diamond, whicwhichh iiss ththee peakpeak ooff ththee first phonophononn sidebandsideband ooff etcetc.. OnOnee musmustt adaddd aatt thisthis poinpointt thoughthough,, thatthat whenwhen ththee H3H3 centrecentre.. ThereforeTherefore,, whewhenn usinusingg onlyonly a handhand AndersoAndersonn publishepublishedd ththee wavelengtwavelengthh ooff a certaincertain spectroscopespectroscope atat rooroomm temperaturetemperature foforr a diamonddiamond absorptionabsorption featurfeaturee havinhavingg measuredmeasured itit witwithh oneone thatthat hashas a strongstrong H3H3 linlinee aatt 503.2nm,503.2nm, oneone couldcould andand confirmedconfirmed itit withwith anotheranother ooff ththee laboratory'slaboratory's mistakmistakee thethe sidebandsideband ooff thisthis centrcentree forfor thethe 496nm496nm excellenexcellentt hand-heldhand-held wavelengthwavelength measuringmeasuring spec­spec­ lineline.. ThereThere araree exampleexampless concerningconcerning otherother gemgem troscopestroscopes,, iinn generalgeneral ththee accuracaccuracyy ofof thathatt measure­measure­ materialsmaterials,, suchsuch aass rubrubyy anandd emeraldemerald,, wherwheree oneone menmentt hahass provedproved,, followinfollowingg checkschecks withwith modernmodern benefitbenefitss fromfrom beinbeingg ableable toto 'read'read'' aann absorptionabsorption spectrophotometers,spectrophotometers, toto bbee remarkablyremarkably good.good. curvecurve ratherrather thanthan observingobserving darkdark oorr brighbrightt lineslines InIn termtermss ooff absorbanceabsorbance anandd transmittance,transmittance, manymany crossincrossingg a narronarroww ribboribbonn ooff colourscolours dowdownn a tube.tube. gemmologistsgemmologists havehave alsoalso trietriedd ttoo describedescribe thethe ultra­ultra­ ThThee laboratory'slaboratory's first responseresponse ttoo ththee probleproblemm inin violetviolet 'spectrum''spectrum' ofof certaicertainn -gemstonesgemstones,, suchsuch asas thethe latelate 1970s1970s was toto installinstall a coolincoolingg uniunitt forfor thethe rubyruby,, emeraldemerald andand diamonddiamond,, byby immersionimmersion contactcontact examinatioexaminationn ooff colouredcoloured diamonds.diamonds. TheThe uniunitt rere­­ photographphotographyy andand usinusingg a short-waveshort-wave ultravioletultraviolet duceducedd ththee temperaturtemperaturee atat whichwhich ththee diamonddiamond was lamp.lamp. ThThee objectivobjectivee beinbeingg ththee separatioseparationn ooff naturalnatural observeobservedd ttoo 120K,120K, aatt whicwhichh temperaturtemperaturee thethe fromfrom syntheticsynthetic andand iinn thethe cascasee ofof diamonddiamond toto 'type''type' absorptioabsorptionn bandbandss becamebecame sharpersharper toto thethe eyeeye andand ththee stonestone aass aann aidaid ttoo identifyingidentifying artificiaartificiall colora­colora­ werweree thereforetherefore easiereasier toto observeobserve.. ThesThesee observa­observa­ tiontion.. tionstions werewere mademade witwithh thethe hand-heldhand-held spectroscopespectroscope InIn thethe modermodernn gemmologicagemmologicall laboratorylaboratory though,though, anandd thereforthereforee wwee stillstill hadhad nnoo conceptconcept ofof ththee 'shape''shape' ththee problemproblemss areare suchsuch withwith modermodernn syntheticsynthetic ofof ththee spectrum.spectrum. WitWithh thethe problemsproblems increasingincreasing allall gemsgems,, andand treatmenttreatmentss toto otherwisotherwisee naturanaturall stones,stones, thethe timetime itit was decideddecided thatthat toto keepkeep aheadahead iinn thethe thathatt evereveryy piecpiecee ooff informationinformation thatthat oneone cacann coaxcoax field wewe hadhad toto obtainobtain a recordingrecording spectrophoto­spectrophoto­ ououtt ofof a testestt iiss needeneededd andand iiff wewe cancan havhavee suchsuch a metermeter.. HavingHaving decideddecided thisthis anandd knowingknowing thethe thingthing asas a 'degree'degree'' ofof accuracyaccuracy,, thenthen thathatt degreedegree limitationslimitations governingoverningg ththee financingfinancing ooff suchsuch a musmustt bebe thethe highest.highest. AnAn exampleexample ofof thithiss wouldwould bebe thethe descriptiodescriptionn ofof thosthosee twtwoo absorptioabsorptionn lineslines whichwhich *A*A phononphonon isis definedefinedd aass a quantuquantumm ofof sounsoundd oror elasticelastic vibrations.vibrations.

© CopyrightCopyright thethe GemmologicalGemmological AssociationAssociation ISSN:ISSN: 0022-12520022-1252 340 J. Gemm.,1989,21,6

Fig. 1. Nicolet model 510 FT-IR spectrometer with 620 work station, plotter and added 8" floppy drive in use at the Gem Testing Laboratory of Great Britain.

purchase, we set about researching the market. in the infrared became more frequent. New types Looking towards the future we hoped to be able to of hydrothermal synthetic emerald, plastic impre­ obtain an instrument at a reasonable cost that gnated opal, synthetic diamond and the answer to would record the spectra of faceted gemstones, those treated yellow diamonds which had been without resorting to destructive testing, for the annealed to higher temperatures to remove the ultraviolet, the visible and the infrared regions. characteristic 595nm line are a few examples. Spectrophotometers are not built taking into The Research Department of the Gemological account a possible requirement ofhaving to record Institute of America obtained a Nicolet Fourier the spectra of faceted gemstones and therefore the Transform Infrared spectrometer and published search for the correct instrument was not an easy some excellent data, and with new hope we began one. In fact when the choice was made we had to the search for an FT-IR unit that would be most accept that the infrared region was going to have to suitable for our needs. In the end, having chosen be a thing for the future, as not only could we not the instrument, we were fortunate enough that one obtain an instrument that gave us all three regions, of our members came forward and bought it for us but even the recording of infrared spectra from - with no strings attached. We now have a Nicolet whole faceted gemstones with a dedicated instru­ model 510 Fourier Transform Infrared Unit (Fig­ ment was unsatisfactory. The instrument obtained, ure 1) which will give us all the information we in the end through subscription and in the mem­ need in the range previously not covered. ory of B.W Anderson,* was and still is one of the best of its type for obtaining spectra from gem­ Increasingly the author is told by gemmologists stones, the Pye Unicam PU 8800 UV/visible spec­ throughout the world to 'keep it simple' so that trophotometer. 'ordinary gemmologists' can understand what is going on. Unfortunately sometimes the black or For some years we faced the fact that the grey boxes are the only answer to some of the infrared area was going to be out of our scope until problems we all face. For the past few years when a new form of instrument was developed that was describing spectra in 'Notes from the Laboratory' more 'in tune' with the requirements of gemmolo- and elsewhere, I have reproduced absorption gy. Then problems in which the answers were held curves rather than trying to attempt drawing what •Opening of Appeal Fund, Journal ofGemmology, XIX, 5, 445. - Ed. might be seen in the hand spectroscope. There has J. Gemm., 1989,21,6 341

been some criticism over this change and people The De Beers and Sumitomo synthetic gem have told me that they cannot understand, but it diamonds really is not that difficult. If one looks down the Both the Sumitomo and the De Beers synthetic left or right hand of the side of the curve it will be gem diamonds have been reported upon in the seen whether the curve was recorded in absorbance English speaking journals, although information or transmittance; if it is in absorbance the sharp on the latter has not as yet been published in these peaks are where dark lines will be seen and the pages. An excellent descriptive paper was pub­ wide bands are where areas of general absorption lished in Gems & Gemology at the end of 1987 may be seen, in the hand-held spectroscope. Along (Shigleyeftf/, 1987). the base of the curve are the units of measurement, During 1988 we were given the opportunity to which for the visible region are normally in examine ten of the De Beers synthetic diamonds nanometres. Apart from displaying a spectrum and, whilst I refer the reader to the aforementioned accurately one should not forget the obvious paper for the expanded detail, with which our advantage in choosing to reproduce a curve, one information and examination mostly concurs, we can easily convert a curve to what might be seen in shall briefly note the characteristics one might the hand spectroscope in the mind but it is not observe with the aid of a microscope or an ultra­ possible the other way around. violet lamp, before seeing how the infrared spectra The move towards the black boxes in some cases of these samples help in their identification. may make a few gemmologists 'uncomfortable' but The samples examined ranged in size from a this latest update to the laboratory's equipment has 0.27 ct yellow emerald-cut to a crystal of 5.24 ct already proved itself many times over with such and the colours were either deep brownish-yellow, problems as synthetic amethyst, synthetic alexan­ yellow or greenish-yellow (Figure 2). Under the drite and amber. A few recent examples are de­ long-wave ultraviolet lamp both the fluorescence tailed in the following paragraphs.

Fig. 5. A metallic needle-like inclusion in a De Beers synthetic Fig. 6. A colourless cross formation in an uncut De Beers diamond. synthetic diamond.

Fig. 7. Fine dust-like inclusions associated with the cross Fig. 8. The De Beers synthetic diamond of Figure 6 between formation of the De Beers synthetic diamond of Figure crossed polarized light. 6. (Dark field). 342 J. Gemm., 1989,21,6

Fig. 2 (top). Faceted and uncut De Beers synthetic diamonds.

Fig. 3 (above, left). The fluorescence of a De Beers synthetic diamond when exposed to short-wave ultraviolet rays.

Fig. 4 (above, right). Fine dust-like inclusions clouding the interior of a De Beers synthetic diamond.

Fig. 9 (left). A natural type lb diamond. J.J. Gemm.,Gemm., 1989,21,6 1989,21, 6 34334 3

RED - NATURAL 'TYPE Ib ' YELLOW DIAMOND SEE FIG . 9 BLUE - DE BEERS SYNTHETIC ·TYPE Ib YELLOW DIAMOND

\

1350.0 1291 . 7 1233.3 1175.0 1116,7 1058.3 1000,0 Wavenumber (em-i)

Fig.Fig. 10.10. A comparisocomparisonn betweebetweenn ththee infraredinfrared spectrspectraa ofof a naturanaturall 'typ'typee lb'lb' yellowyellow diamonddiamond anandd a DDee BeersBeers syntheticsynthetic typtypee lblb yellowyellow diamonddiamond.. BotBothh curvecurvess araree recorderecordedd inin absorbance.absorbance. 344 J. Gemm., 1989,21,6 and phosphorescence varied from sample to sam­ single row of coated amber beads, a pair of interest­ ple. The more brownish stones were inert to this ing amber earclips were also submitted. wavelength, the yellow stones tended to have a As these were not coated with an 'artificial' weak orange glow, with one stone being inert, and substance, we shall deal with the amber in the a clear phosphorescence (apart from one stone), earclips first. They were a rounded cabochon and the greenish-yellow stones each displayed a shape, the metal earclip was attached to the flat moderate to clear phosphorescence whilst the side, and the colour was approaching orange. The fluorescence varied from almost inert to weak. metal fitting, being attached with an adhesive, Again under the short-wave ultraviolet lamp the prevented an SG determination and as there were response was varied. The brownish stones tended no inconspicuous areas where an olfactory test to have an orange background with distinct yellow could be facilitated this too was initially ruled out. zones which corresponded with the cubic growth An estimation of the refractive index by the distant sectors, (Figure 3), whilst the yellow stones were vision method put this constant in the region of either a moderate orange with no phosphorescence 1.54. The material was 'cloudy' but contained no or a distincdy zoned strong yellow with a strong inclusions which would assist in identification. phosphorescence. The greenish-yellow stones were On the back of one of the cabochons it was either a zoned yellow or a moderate orange, but in noticed that a small sliver of the material had both cases the phosphorescence was strong. parted from the main body but was being held, in Material observed within the stones included place by, and under, the metal fitting. As the sliver dust-like particles (Figure 4) and metallic inclu­ was not 'attached' to the main body of the 'amber', sions (Figure 5). Yellow/colourless zoning within with the careful use of a fine pair of tweezers we these synthetics (Figure 6) relates to the nitrogen were able to remove it. In doing so we discovered content in various growth sectors. When seen this that the colour was concentrated at the surface, zoning may serve as a first warning of a possible whilst the centre was colourless (Figure 11). The synthetic origin and when observed a little more colour was not a coating of an artificial substance closely as in Figures 6 and 7, it may be seen that but was actually a part of the surface. This is a tiny dust-like inclusions are orientated with this feature which we have noted before in heat treated zonal structure. When observed between cross amber (Scarratt, 1986). In order to confirm its polarized light a distinctive cross-like pattern may identity a small scraping was taken from the inside be seen (Figure 8 [which relates to Figures 6 and colourless part of the sliver and an infrared spec­ 7]). trum was taken from this. The resulting spectrum The infrared spectra observed for all of the De was characteristic of amber. The process from Beers synthetic stones were distinctive in that they taking the scraping to obtaining the spectrum (see revealed the characteristic peak for dispersed nitro­ Figure 12 (1)) took no more than five minutes. gen (type lb diamond) and there were no signs of The artificial coating on the surface of the beads the peaks associated with aggregated nitrogen in the necklace was quite obvious when examined (common to IaA and IaB diamonds). In natural lb with either a lOx lines or a microscope (Figure 13), diamond it seems that almost invariably the peaks but identifying the material underneath would due to aggregated nitrogen are found to be present have been difficult if we were only to conduct the along with the dispersed nitrogen peak. This is normal gemmological tests. clear when one looks at the example in Figure 9, The beads appeared to be an orange colour but which is a natural type lb (canary) diamond with a in a number of places, around the ends of the drill visible spectrum similar to that of a synthetic holes, the coating had come away to reveal that the yellow diamond, i.e. one of continuing and gradual material beneath was coloured yellow (Figure 13). absorbance towards the shorter wavelengths. The A scraping was taken from the bead underneath infrared curve of this stone shows a clear peak due the coating and as revealed in Figure 12 (2) the to aggregated nitrogen (Figure 10) whilst a De infrared spectrum produced from this was found Beers synthetic stone of a similar colour, as com­ to be that of amber. Interestingly, upon taking this pared in Figure 10, shows only the dispersed scraping we discovered that the yellow colour of nitrogen peak. the bead was also a 'surface only' colour. The bead was colourless underneath, it had a yellow surface probably due to heat treatment, and on top of this Coated amber was an artificial coating which was orange in On two occasions recently we have been asked to colour. identify material which has turned out to be coated amber, and infrared spectroscopy has helped in its identification. On the first occasion apart from a J.J. Gemm.,Gemm., 1989,21,61989, 21, 6 345345

2.

1.

1850.0 1666.7 1483.3 1300.0 1116.7 933.33 750.00 Wavenumber (em-i)

Fig.Fig. 12.12. TheThe infrareinfraredd spectraspectra ofof twotwo piecespieces ofof amberamber bothboth recordedrecorded iinn transmittance.transmittance. (1).(1). AnAn amberamber earcJip,earclip, andand (2)(2) anan amberamber beadbead whichwhich hadhad anan artificalartifical coatingcoating (the(the scrapingscraping beingbeing takentaken fromfrom ththee beadbead belobeloww thethe coating).coating). 346346 J.J. GemmGemm..,, 1989,21,61989, 21, 6

Fig. 11II.. A smalsmalll slivesliverr ooff amberamber removeremovedd frofromm anan earc1ipearclip Fig. 13.. A coatecoatedd ambeamberr beabeadd showingshowing aann areaarea wherwheree thethe showingshowing ththee colourlescolourlesss interiointeriorr anandd colouredcoloured exterior.exterior. coatincoatingg hashas comecome away.away.

NaturallNaturallyy colouredcoloured greegreenn TypeType lilIbb diamonddiamond browbrownn colour, wawass eitheeitherr thathatt typicaltypical ofof a brownbrown WWee mostlymostly thinthinkk ofof typetype lilIbb diamonddiamondss aass beingbeing typtypee lIaa stonestone oorr thathatt ofof a Iblb stone.stone. ThThee resulresultt was a blubluee iinn coloucolourr althougalthoughh colourlesscolourless andand colourless!colourless/ littllittlee liklikee a typtypee lIbb curvecurve,, witwithh increasinincreasingg absorp­absorp­ browbrownn zonezonedd stonesstones havhavee beebeenn reportedreported.. A shortshort tiotionn forfor ththee shortershorter wavelengthwavelengthss frofromm abouaboutt 520nm520nm timtimee agagoo anan octagonallyoctagonally shapedshaped facetefacetedd diamonddiamond bubutt witwithh a widwidee absorptioabsorptionn 'hump'hump'' stretchinstretchingg fromfrom weighinweighingg 5.805.80 ctct wawass submittedsubmitted forfor examinationexamination 525200 ttoo 460nm460nm anandd peakinpeakingg aatt 49Onm.490nm. ThThee areareaa ooff (Figure(Figure 14).14). ThThee coloucolourr ooff ththee stonstonee wawass a littlelittle leasleastt absorptioabsorptionn wawass iinn ththee greengreen,, aass mighmightt bebe difficult ttoo describedescribe,, howeverhowever:: iinn a standarstandardd diadia­­ expectedexpected,, bubutt thethenn unlikunlikee lIbb stonestoness ththee absorbanceabsorbance monmondd gradingradingg lighlightt boboxx greygrey,, browbrownn anandd greengreen levelevell beginbeginss ttoo risrisee agaiagainn for ththee longelongerr wavelengthswavelengths colourcolourss coulcouldd bbee seenseen;; undeunderr a bencbenchh lamlampp fittedfitted frofromm 620nm620nm.. ThThee levelevell ooff absorbancabsorbancee aatt 750n750nmm witwithh a tungstetungstenn bulbulbb jusjustt greegreenn anandd browbrownn couldcould beinbeingg slightlslightlyy mormoree thathann halhalff thathatt aatt 390nm.390nm. bbee seenseen;; anandd iinn ththee normanormall laboratorlaboratoryy lightinglighting,, i.ei.e.. ThThee spectrumspectrum,, iinn whicwhichh thertheree werweree nnoo sharpsharp daylighdaylightt fluorescentfluorescent tubestubes,, botbothh gregreyy anandd greengreen peakspeaks,, dididd nonott falfalll intintoo a convenienconvenientt categorycategory,, bubutt coulcouldd bbee seenseen.. ThThee predominanpredominantt coloucolourr appearedappeared ththee nexnextt testestt gavgavee uuss a clucluee ttoo ththee typtypee ooff stonstonee wwee ttoo bbee greegreenn iinn mosmostt instanceinstancess bubutt iinn somsomee circum­circum­ werweree dealindealingg withwith,, anandd iitt wawass fafarr frofromm whawhatt wwee stancestancess browbrownn predominated.predominated. werweree expectingexpecting.. UndeUnderr botbothh long-wavlong-wavee anandd short­short­ AparApartt frofromm makinmakingg observationobservationss oonn ththee colourcolour wavwavee ultravioleultraviolett lighlightt ththee stonstonee appeareappearedd ttoo bbee inertinert anandd examininexaminingg ththee stonstonee witwithh ththee aiaidd ooff a micromicro­­ bubutt whewhenn ththee short-wavshort-wavee lamlampp was switcheswitchedd ofofff thethe scope, ththee firsfirstt testestt carriecarriedd ououtt oonn ththee stonstonee wawass ththee stonstonee displayedisplayedd a stronstrongg blue-greeblue-greenn phosphor­phosphor­ recordinrecordingg ooff ititss visiblvisiblee spectrumspectrum.. ThThee typtypee ooff escenceescence.. ThiThiss beinbeingg a typicatypicall characteristicharacteristicc ooff typtypee spectruspectrumm wwee werweree expectingexpecting,, judginjudgingg frofromm ththee parpartt lilIbb blubluee diamondsdiamonds,, wwee thethenn testetestedd ththee stonstonee forfor electro-conductivityelectro-conductivity.. AparApartt frofromm confirminconfirmingg thathatt ththee stonstonee was a conductoconductorr ooff electricityelectricity,, ththee testestt proveprovedd ttoo bbee quitquitee dramatidramaticc witwithh blubluee flashes comincomingg frofromm withiwithinn ththee stonstonee almosalmostt frofromm ththee instaninstantt thathatt contaccontactt wawass mademade.. ThThee infrareinfraredd spectruspectrumm wawass thethenn taketakenn anandd comparecomparedd witwithh otheotherr typtypee lilIbb spectrspectraa filefiledd iinn ththee computercomputer.. ThThee spectruspectrumm ooff thithiss stonstonee wawass ththee samsamee aass thosthosee recorderecordedd previouslpreviouslyy foforr typtypee lilIbb blubluee stones.. ReferenceReferencess Scarratt,, K.,, 1986.. NoteNOless frofromm ththee LaboratorLaboratoryy -- 6. 6. JournalJournal of Gemmology,Gemmology, 2020,, 22,, 9595.. ShigleyShigley,, J.E.J.E.,, etet al.,al., 19871987.. ThThee gemologicagemologicall propertiepropertiess ooff ththee DeDe Beers Beer sgem-quality gem-quality synthetic synthetic diamond. diamond. Gems Gems& & Gemology, Gemolo­ FigFig.. 14.. A green/browgreen/brownn (colou(colourr dependindependingg upouponn lightinglighting)) typtypee 23gy,, 4,23, 187-206. 4, 187-206 . lilIbb diamonddiamond.. 5.85.800 ctct.. [[ManuscriptManuscript receivedreceived 25 January 1989.J1989.] J. Gemm., 1989, 21, 6 347

Proceedings of the First International Amber Symposium

Helen F taquet, FGA

London

Fig. 1. Natural freeform amber necklace with pressed amber rods, pendant and bead.

Summary Introduction Sixty participants from Europe, USSR, Africa and This was in fact the sixth meeting on Amber and USA, were invited to the first International Amber Amber-bearing sediments to be held in Poland, but Symposium, hosted by the Museum of the Earth, the first of an international nature. Accordingly, Warsaw, in October 1988. much of the Symposium explored areas of future Twenty-seven papers were offered, covering all mutual exchange of samples and scientific papers. aspects of the sciences and arts in relation to this fossil resin, in four working languages - German, Russian, The first two papers - 'The present status of English and Polish. research of amber and other fossil resins' (Saw-

© Copyright the Gemmological Association ISSN: 0022-1252 348 J. Gemm., 1989,21,6 kiewicz, S., Leningrad) and The significance of sive paper about East African copal - and confirmed museum collections of amber and other fossil resins' the author's view that very little copal has ever been (Kosmowska-Ceranowicz, B., Warsaw), explored used as jewellery. the possibilities opened up by the global political Migaszewski, Z. (Kielce), showed current inves­ thaw of the late 1980s, especially with regard to tigation into black resins, jet and the new appear­ re-examining existing collections, many of which ance on the market of black amber jewellery. The had been transferred across Europe during the latter is being produced by a Co-operative south of progress of the two World Wars. Warsaw with a source material of processed succi­ By cross-referencing experiences it became ob­ nite. The streak mark left by this manufactured vious that an extensive catalogue of the amber substance is black, the lustre is good, and under a contained in various national collections would be a microscope there are to be seen two distinct mate­ great step forward for both those working as rials - dark grey particles cemented by a very fine art-historians and in the sciences. This is especially grained light grey substance. so, as many former great collections are now split The Museum of the Earth in Warsaw has two between various museums. For example, that of the samples of stantienite collected from the Palmnick- Albert University in Königsberg (Kaliningrad) en deposit in 1880. These have a velvet black colour, which once comprised 70 thousand specimens, is a brown to light brown streak, and under the thought to be split between the University Museum microscope a structureless groundmass of dark grey in Goettingen, the Natural History Museum of containing 'yellow-orange and blood red inner Humboldt University in Berlin, and the British reflections'. Museum of Natural History in London. During the Also in the collection are two samples of soft fossil course of the conference it was learned from Dr resin from Lower Miocene deposits of the Ukraine Katinas, that his nation's Lithuanian Amber and Bitterfeld. The microscope reveals a structure­ Museum at Palanga would be opened to the West for less, porous cracked lustreless resin of black colour the first time. yielding a dark greyish-brown streak. The samples New finds have the same reflections as above with the addition Several new sources of amber were reported of scattered fragments of crushed plant tissue. during the conference. Kosmowska-Ceranowicz A third type of black resin is represented by a and Krumbiegel, G. (Halle), presented a joint paper sample from Bitterfeld and another from Bytow in on Bitterfeld amber, a Miocene deposit (22 million Poland, whilst there are at least three pétrographie years old) mined near Leipzig in East Germany, of varieties of jet assigned to the Lower Jurassic from which a proportion goes into the production of Odrowaz in Poland. jewellery. The amber shows the usual colour range, Black resins were thought in the nineteenth clear and cloudy, etc. Sokolowa, T (Leningrad), and century to originate from fire in the forest at the Rasnitsyn, A. (Moscow), described four types of time of formation. However, the authors of this Cretaceous amber recovered from field trips to 1988 paper consider lightning to be a more likely Northern Siberia and the Arctic Sea in the 1970s. theory. Some of the pieces appear to be similar to gedanite, Other scientific papers and all are too fragile for decorative purposes, The majority of those present at the Symposium although the inclusions are naturally of great in­ represented the sciences of geology, mineralogy and terest to paleo-entomologists and botanists. A third paleontology. However, many of the papers proved find of Upper Cretaceous amber was also reported interesting across traditional boundaries. To this from Alberta in Canada. end gemmologists should find useful 'Comparative Regional updates were offered from Romania, studies on micro-elements in amber' from Sicily and the Dominican Republic, as well as from Koziorowska, L. (Warsaw), which included data areas less familiar to the gemmologist such as such as the presence of silver amongst Baltic amber, Bulgaria and Nigeria. This last is an Eocene resin but not that from Sicily or the Dominican Republic. with a chemical structure shown by IR spectra to be Also 'Gas chromatography - an effective tool for a new species. It has been given the name Amekit. chemical characterization of fossil resins', Vavra, N. Perhaps the most obscure piece of amber to be (Vienna). This may prove to be a rapid method of discussed was a single nodule found at a depth of investigation, which already differentiates samples 2,302 m below sea level during the course of deep from within the Dominican Republic. 'The pres­ drilling in the Persian Gulf. Its infrared spectrum is ence of vertebrates and their remains in amber', identical to that of Rumanite from Romania. Sever­ Poinar, G. (Berkeley), should also be required al of the core samples contained this resin, but only reading for all those faced with abnormally large one sample was analysed. inclusions brought in by members of the public for Schlüter, T. (Dar es Salaam), gave a comprehen­ verification. JJ.. Gemm.Gemm.,, 1989,21,61989, 21, 6 349349

Fig.2(a)

Fig.2(b) Fig.2(c)

Fig.Fig. 2 (a,(a, b andand cc)) InteriorInterior ofof thethe BursztynyBursztyny amberamber co-operative,co-operative, Gdansk,Gdansk, Poland:Poland: (a)(a) visitingvisiting thethe grindinggrinding andand polishingpolishing room;room; rodsrods ofof pressedpressed amberamber awaitingawaiting despatch;despatch; (c)(c) thethe productionproduction areaarea forfor heatingheating andand pressingpressing amberamber intointo rodsrods (the(the samsamee equipmentequipment isis usedused forfor producingproducing amberamber witwithh stress-inducestress-inducedd inclusions).inclusions). 350 J.Gemm., 1989, 21, 6

Field Expedition to Gdansk and Malbork round or oval beads. The major colours represented The two days of presentations were followed by a are bright yellow (natural) or syrup/brown (press­ weekend field trip to the coast. In Gdansk the party ed). There are same animal carvings of elephants, was able to join those working to extract amber from tortoises, etc. One exception to this general dull marshland with the aid of hydraulic hoses. The conformity was the use of thin-slab amber with amount of amber washed out from the reed-bed silver in tie-clips, and brooches by a single shop in deposit was surprisingly high, and paid the wages of Gdansk. The lack of general flair is understandable ten people on that site alone. The land was owned given the isolated nature of the country. However, by a nearby factory and had been leased by an one is left with the impression that Poland is amber processing co-operative in the town of rebuilding, despite the system. Gdansk (Figure 2). The hosts of this meeting in Warsaw only started The co-operative was open to our detailed ques­ collecting amber in 1951, yet today house one of the tioning - the operatives making round and faceted largest hoards of natural resin in Europe. The beads on simple rotating laps had been thus em­ Archeological Museum in Gdansk overflows with ployed for up to 22 years, and coloured rods of amber finds made in the last few years, and the pressed amber had been manufactured in black, National Collection of Amber Artefacts at Malbork green, red, sand, etc., as well as the usual two-tone Castle already occupies a whole gallery. There is an swirled syrup since 1981. Although the author's infuriating lack of pin-point dating at the latter two overall feeling was one of depression, at least the institutions, and one or two gross errors - for larger, and purer specimens of amber were sorted example a whole display of phenol formaldehyde out, after an initial clean, and reserved on one side plastic beads, described as Sicilian Amber, but the not to be pressed but to be used without further academic enthusiasm is contagious. processing. Although not seen, the factory Thanks must be given to all those who made this apparently produced sun-spangled amber from Symposium possible. Summary papers are available time to time, using different time and pressure from the author, and it is hoped that before too ratios. many years elapse Britain will herself come forward There is much amber jewellery for sale in Gdansk to host such an event. and in the larger international hotels. It is expen­ sive, and disappointingly unexciting. Very little is polished freeform (as is the necklace illustrated in Figure 1), most being non-graduated or graduated [Manuscript received 26 January 1989.]

NEW GEMMOLOGY COURSE The Gemmological Association of Great Britain is proud to announce that it has introduced a new home study course in gemmology. This prepares students for the examinations leading to the award of the Association's Fellowship Diploma. The new course is radically different from other gemmological courses, and presents a new, friendly, step- by-step approach to learning that should be welcomed by students all over the world.

F or further details, contact the Education Department, Gemmological Association of Great Britain, Saint Dunstan's House, Carey Lane, London EC2V 8AB. Tel: 01-7264374. Cables: GEMINST. J. Gemm., 1989, 21, 6 351 The Dresden Green

G. Bosshart

Swiss Foundation for the Research of Gemstones SSEF*, Zurich

* Schweizerische Stiftung Für Edelstein-Forschung (SSEF)

Introduction Once upon a time there lived a king. He was tall, strong, and immeasurably wealthy since his ancestors were already Fleece by the Dresden court jeweller J. F. Dinglin- in possession of productive silver mines. He did not waste ger. However, in 1746 it was reset 'à jour' by the his treasures on foolish wars. On the contrary, he Genevan jeweller A. J. Pallard at the court of Vienna accumulated riches in the safe vaults of his castle of such (open-back bezel setting as in Figure 3) and in 1768 vastness that his kingdom became renowned and was finally mounted by Diessbach into the hat brooch admired far and wide. known to the present day (Figure 2). The Dresden Green remained in the Green Vaults for over two centuries until, due to the Second This is not the beginning of a legend but a sketch World War, all Art Collections of Dresden were ofwhat happened in the seventeenth and eighteenth moved up to the Königstein (King's Rock), the centuries prior to and during the reign of the Saxon imposing grey mountain fortress at the entrance to Elector August II, also named August the Strong the Eibsandsteingebirge (Sandstone Sierra of the (with the exception of the wars). His residential Elbe River region). From there the Soviet Trophy cities were Dresden and, after his coronation as Organisation (Copeland, 1966, 25) transported the King Frederick August I of Poland, also Warsaw. Collections into the subterranean safes of the USSR The accumulated riches of gold, silver, jewels, Ministry of Finance at Moscow (Menzhausen, curiosities, and in particular gemstones, were 1987a) shortly alter the war. They were handed out arranged and stored below his residential palace in to the German Democratic Republic in 1958. Since vaults painted green. These rooms soon came to be then the Collections have been conserved and known as the Green Vaults (Grünes Gewölbe). They displayed mostly at the Albertinum and in the served as strong-rooms and, in anticipation of a Zwinger. The State Art Collections of Dresden as coming era, also as a treasury museum, fitted as an much in their totality as also in their parts, e.g. the elegant French-style mirror cabinet (1723-1724). In Saxon-Polish Crown Jewels of the Green Vaults or the following years, the copper-plate engraving the Meissen Porcelain, are unique worldwide, but cabinet, the gallery of paintings, the collection of surprisingly little known, even in Europe. porcelain and the collection of natural sciences were It has come to be considered the destiny of many founded and exhibited in the pavilions of the famous diamonds that their histories remain un­ Zwinger, stronghold of the former fortress. known or fragmentary at most. In the case of the (Menzhausen, 1987a, 1988.) For good reasons, Dresden Green this concerns its trade route before Dresden was known as the Florence of the Elbe 1741 and the sojourn from 1945 till 1958. It is River. assumed that the stone originated in India rather In 1741, the son of August the Strong, Elector than in Brazil. August III of Saxony (since 1733 King Frederick The rarity of the Dresden Green is based not so August II of Poland), bought one of the rarest much on its weight, which is over 40 ct, but rather diamonds from a Jewish dealer. Together with the on its green colour. In reality however, it is the Diamond Suite (Copeland, 1966,29), the green gem coincidence of both properties that makes the was registered as No. 50 in the inventory of 1733 (cf diamond so exceptionally rare. Up to the present transcription below Figure 1). From then on, the day, it has remained the largest cut diamond of diamond was known by the name of 'Dresden natural green colour on record. Over the centuries it Green Diamond' or shorter 'Dresden Green' and has not lost anything of its celebrity status. But on 'Green Brilliant' (Table 1). In 1742 this brilliant-cut the contrary, it has become of increasing cultural stone was mounted into the Order of the Golden interest and, recently, also of great scientific value.

© Copyright the Gemmological Association ISSN: 0022,1252 352 J. Gemm., 1989,21,6

Fig. 1. Hat ornament (brooch) belonging to the Diamond Suite of the Elector August III of Saxony, displayed on the original volume of the 1733 Inventory of the Green Notandum Vaults. Das izo unten anhangende goldene Lamm- Transcription of the Registration No. 50 in the Inventory Fell, nebst denen drey darin versezten Brillan­ (written in elderly chancery language, Pfister, 1988) ten gehöret zu dem mit Katzen-Augen versez­ ' [Seite] 89. Andere Schranck Lit: B. ten Toison, wo es bereits eingetragen zu befin­ Sechstes Brett: pag: 202. den, vide abg. und Verw. Schein vom 31. July Eine große Brillanten Gar. 1743. [Seite] 90. nitur. N°. 50 Dieser Toison ist a°. 1745. von Praag aus nach Wien, um daselbst ganz neu gefertiget zu N°. 50 Ein Orden des goldenen Vließes bestehet in werden ge schicket worden, Der grüne große einem großen und extra schönen grünen oval brillant ist wiederum im neuen Vließ Orden länglichten Brillant um und um mit kleinen angewendet und [als] N°. 55 bey dieser brillan­ Brillanten carmisiret. [umrandet, eingefasst] ten garnitur eingetragen. [Neufassung durch Die Flammen zu beyden Seiten sind theils mit den Genfer J. Pallard, 1746] Die Flammen und kleinen Brillanten besezt, theils roth email- der Schnirkel [Schnörkel] aber N°. 42 und 43. liret. zum Vorrath an Brillanten geleget worden. Die Der Haken ist als ein Schnirkel façoniret und Einfaßung um den großen grünen Brillant mit vielen kleinen Brillanten besezt. In der aber, so über und über mit kleinen brillanten, Mitten aber ein mittler viereckigter Brillant haben S. Königl. Mait. zu hohen Händen verfaßet. behalten. Der grüne Brillant, ist von dem Juden Delies C. Verwahr, und abg. Schein vom 31. Jan: 1741. gelieffert worden, und hält am Gewichte 1748. 160. green, [von engl, grain?, ca 40 et] C. G. Cleichmann. [?] Der Toison aber ist von dem Hoff-Jubelier Dinglinger geferttiget und 1742. zum grünen N°. 51 Ein paar goldene Hand-Hembden-Knöpfgen Gewölbe geliefert worden [Watzdorf 1962] mit zwey Brillanten besezt...' J. Gemm., 1989, 21, 6 353

|_ Table 1. Physical Properties of the Dresden Green Diamond CUT Pear-shape with rounded tip (almond-shape), historic brilliant-cut style (pear-shaped old-cut brilliant)

Measurements Length x Width x Height approx. 30.30 x 20.35 x 10.288mm of diamond (TESA dial calipers and micrometer) Table T approx. 16.30 x 10.15 mm (SSEF CuletC approx. 3.25 x 1.65 mm table gauge)

Proportions Table width/Width 49.9% Culet width/Width 8.1% Height/Width 50.6% Crown height/Width approx. 17% (estimated) Pavilion height/Width approx. 33% (estimated) Girdle width/Width approx. 0.5% (where visible), i.e. very thin to sharp-edged L/W approx. 3/2 H/W approx. 1/2 TW/W approx. 1/2 TW/TL approx. 1/1.6 CW/CL approx. 1/2 Cr / Pv approx. 1/2 Symmetry Good to very good: no large remnants of crystal faces ('naturals') or extra facets present, very sharp facet corners; bezel and pavilion (upper and lower main) facets in part slightly distorted, girdle slightly wavy

Polish Good to very good: table facet perfectly plane; some light wheelmarks

Measurements Gold bezel LxW approx. 30.90 x of bezel 20.60 mm Height 1.90 to 2.40 mm (without prongs) Silver bezel Height 3.30 to 3.80 mm (pavilion) Thickness 0.48 to 0.51 mm Four drillholes for 'lacing' the silver bezel into the hat ornament (brooch) using silver wire (Arnold, 1988) drillhole diameters from 0.7 to 1.3 mm Condition Girdle of diamond mediocre: numerous small breakages, girdle projecting over the gold bezel on almost half of the circumference (from right to top) and extremely thin. Bezel setting good: excepting a fine-grained layer on the gold bezel at top right, on right side and bottom left (Figure 3, remainders of tin solder rather than oxidized silver solder; no patina) WEIGHTS Al approximately 41.1 ct (author's calculation by of the means of similarly proportioned pear-shaped old- Dresden cut brilliants as Green length x width x height x 0.0065) A2 approximately 43 ct (too high; calculation on the basis of the conversion factor 0.00678 for a loose pear-shaped old-cut of 13.24 ct of the Green Vaults) 354 J. Gemm., 1989,21,6

B1 41 ct (Green Brilliant, Menzhausen 1987a) B2 Dresden Green, identical with Green Brilliant, i.e. 41 ct (Menzhausen, 1987b) CI 41.00 ct (Dresden Green, De Beers, 1983,60) C2 40.00 ct (Green Brilliant, De Beers, 1983, 60), citation of erroneous indications in the Anglo- Saxon literature (Copeland, etc.) Dl AXVi ct (Bauer, 1896,157), contradiction to D2 D2 40 ct (Bauer, 1896,287 : 'not 31 VA or 48 carat') E 160 green (Inventory volume 1733), [green = engl, grain (?), between 40 and 41 ct]

Weight including 11.182 g (55.91 ct) bezel setting (Owa laboratory balance 160 g max., e = 0.01 g)

PURITY External characteristics One small extra facet at the tip of the pavilion, one very small natural near the girdle on the right of the crown side

Blemishes Numerous small to tiny breakages along the girdle on the crown and pavilion side, one short curved scratch on the left in the table, some slightly abraded facet edges on the crown and pavilion side (Hänni and Bosshart, 1987)

Internal characteristics One small, concentrically ribbed tension fissure of a whitish appearance and similar to a healing crack and one shallow and short fissure with green specks (Figure 7), both on the left of crown near the girdle; very short tension fissures with green spots on the right of crown at the girdle, one group of tiny, brown reflecting opaque crystal inclusions (chromian spinels?) near a lower girdle facet on the right (approx. 0.15 mm deep)

Growth characteristics Weak to distinctive, lamellar zoning in triangular octahedral arrangement (three-point diamond)

Strain birefringence Fine, cross-hatched and pronounced, lamellar extinction pattern in cross-polarized light ('Tatami' type, Orlov, 1977, \ 16), no interference colours

Damages One small tension fissure emanating from a girdle chip on the right crown side, one tiny percussion mark in the bezel at the tip

Purity grade SI (small inclusions, CIBJO Rules 1986), theoretical possibility of improvement of the purity and girdle by a professional repolishing operation.

1 COLOUR Description Transparent, non-fluorescent slightly bluish-green of weak saturation

Colour grade Fancy colour J. Gemm., 1989, 21, 6 355

Classification After the Colour Atlas DIN 6164 (Biesalski, 1957) as colour index triplet < < hue : saturation : greyness > > body colour K (in transmitted light) —21 : Vz : 1 reflection colour R (in reflected light) ~ 21 Vi : 3 ± 2: 3 reflection colour R (Rösch, 1969) ^22 :2 - 3 : 3

Colour distribution Apparently homogeneous body coloration (no colour zoning, mottled or surface colour)

Colour type Natural coloration (Menzhausen, 1987b)

Cause of coloration Light absorption (GR 1-8) at a limited number of crystal lattice defects, generated by a continued natural radioactive irradiation in the diamond deposit; annealing in the parent rock at a maximum of 3 5 0°C

Colour stability Possibility of fading of the green coloration by thermal healing of the GR 1-8 lattice defects starting at about 500°C (Woods and Collins, 1986)

UV Fluorescence Weak, impure yellowish-green, homogeneous (VEB Quarzlam­ pen markkleeberg UA 150.1, 365nm/140W/10cm)

ABSORPTION UV/VIS GR 1 very weak absorbance band from 750 Figure 6 to 530 nm, with medium strong zero- phonon doublet (Collins, 1982) at 741.0 and 744.3 nm 667 very weak line at 666.6 nm (after Davies, 1977 stable below 700K/430°C) 594 extremely weak band at 594 nm (appears above 275°C only, Woods and Collins, 1986) 495 very weak band at 495 nm 473 very weak band at 473 nm TR 12 very weak line at 470.1 nm GR2-8 weak to extremely weak lines at 430.4, 429.5,419.1,413.2 nm, etc. RIO very weak line at 393.5 nm R 11 weak line at 310.8 nm 306 very weak line at 306 nm 303 very weak line at 303 nm 289 very weak line at 289 nm 279 extremely weak band at 279 nm 225 steep and high absorption edge at 225 nm

MIR No specific absorption bands in the middle infra-red region (4000 to 400 cm"1 / 2.5 to 25 /xm) except the strong lattice absorption present in all diamonds between 2650 and 1400 cm-1 (Davies, 1977) -* TYPE Ha

RADIOACTIVITY No residual ß/y-activity observed (background 0.2 counts/sec on Geiger counter EMA GZ25/VA-Z125)

CONDUCTIVITY Thermal conductor (EICKHORST Thermolyzer II), electrical insulator (voltmeter)

DIAMOND TYPE Ha 356 J. Gemm., 1989, 21, 6

Modern investigations of the Dresden Green diamond and interpretation of the results Motivated by the contributions of Collins (1982) and Orlov (1977) on the one side and by Bauer (1896) and other writers of the past century on the other, the author applied for permission two years ago, to investigate the Dresden Green extensively by modern, non-destructive gemmological and analytical methods. A unique authorization was granted from 22 until 24 November 1988 to him as well as to R. E. Kane and S. F McClure. These colleagues of the Gemological Institute of America jointly and shortly will report on the history and gemmological properties of the diamond and will publish professional colour reproductions. Colour Testing In addition to the urgently needed characteriza­ tion of such a prominent diamond individual by weight, measurements, proportions, etc., the inten­ tion was to find out whether the Dresden Green belonged to the 'relatively rare, uniformly bottle- green' diamonds (according to Orlov) or whether it possessed, as Bauer put it, a Very nice, light apple-green' colour (or even an 'oil-green, yellow- green, pale, leek, asparagus, pistachio, olive, siskin, emerald, bluish or greyish-green colour'?) The question is what sort of bottles and apples they meant. According to the Identity card of the Diamond (Table 1), the colour hue is definitely a Fig. 2. Hat ornament exhibiting the sumptuous principal bluish-green. stone, the Dresden Green. Magnification 0.8x Collins (1982) confirmed that uniformly green (by this he did not mean surface-coloured but body-coloured green) diamonds are so rare that up to now no corresponding absorption spectra existed in literature. According to Collins, however, these spectra would be of scientific importance to solid state physicists for the clarification of the natural causes of green coloration (e.g. irradiation), as a possible precursor of yellow and brown colorations (annealing during or subsequent to irradiation). In addition it would be a breakthrough of commercial significance if specialized gemmologi­ cal laboratories henceforth would be in a position to differentiate between diamonds of natural and artificially caused green colour. At present few laboratories succeed in reliably identifying these colorations and then only in exceptional cases. For these reasons the author has pursued his goal for over three years now (outside the daily routine analysis of gemstones) to trace cut diamonds of guaranteed naturally green colour - this proved to be unusually difficult - and to measure them accurately. The research work will come to a close soon and will then be published (Bosshart, 1989).

Fig. 3. The Dresden Green set in an eighteenth century gold Absorption Analysis (and silver) bezel and scintillating in all spectral colours. In some of the recognized gemmological labora­ Magnification 3 x. tories it has been standard practice for more than J. Gemm., 1989,21,6 357 ten years now to record the absorption spectra of coloured diamonds applying refrigeration by liquid nitrogen (boiling temperature of LN2 at atmospher­ ic pressure: -196°C/77K, where Kelvin (K) = Celsius (0 C) + 273.16). The advantages of this procedure are absorption diagrams which give much increased evidence compared to the spectra registered at ambient temperature (Collins, 1982), as is proved by Figure 4: Survey spectra: upper blue curve- medium refrigeration lower blue curve - weak refrigeration red curve - ambient temperature (horizontal red line: baseline of spectrophotometer and cryogenic cell)

Figure 5 presents the well established cooling cell of the bath type developed by the author. In contrast to the cryogenic flow type devices of other labora­ tories cooling the diamond with nitrogen gas cros­ Fig. 4. The first three absorption spectra ofthe Dresden Green sing the spectrometer sample beam at right angles Diamond showing lesser spectral information in the red curve registered at ambient temperature than the spec­ (Scarratt, 1979, and Hoferand Manson, 1981), the tra run at freezing temperatures (blue curves). Baseline Dresden Green was mounted in the Nrvapour of spectrophotometer and cryogenic cell (horizontal, atmosphere of the illustrated highly-transparent red) and absorption curves vertically displaced for cooling cell (i.e. above the liquid nitrogen bath) in better understanding. such a manner that the diamond could be traversed by the light beam on a linear optical path. lt was and is a favourable and rather unusuai circumstance that the Dresden Green, still mounted in its bezel setting, possesses a large culet facet parallel to the table facet. The optical path length between table and culet, however, was the absolute­ ly shortest of the stone, corresponding to the weakest possible absorbance (cf Figures 3 and 6). On the other hand, the light traverse in the long or diagonal directions of the diamond was rendered practically impossible by the silver bezel hiding the pavilion of the diamond just below the girdle. The 'Dresden Green Project' was consented to only after the author's party had fl.lrnished physical evidence that the necessary refrigeration (and sub­ sequent warming up) could cause darnage neither to the diamond nor its green coloration nor the bezel setting (Rosenfeld and Bosshart, 1987, etc.). De­ spite the author's many years of experience in refrigerating ]arge and small, mounted and loose diamonds, there remained a residual risk which needed a little courage to overcome since doubts about the innocuousness of the project for the famous large diamond had been expressed in some gemmological circles. Although the present inves­ tigation has been completed successfully and with­ Fig. 5. The Dresden Green mounted in the N 2 vapour atmo­ out detriment to the diamond and its setting, this sphere of the highly transparent cooling cell and still must not be interpreted as an encouragement to adjusted in the sample beam of the Pye Unicam SP8- 100 UV IVIS spectrophotometer prior to the deep-freeze gemstones unscrupulously as certain first absorption measurement in refrigeration. significant conditions have to be fulfilled. 358358 JJ.. Gemm.,Gemm., 1989,21,61989, 21, 6

Abs"rption spectrum of the deep·'rozen diamond (41 etl recorded at high resolution on • Pye Unlearn SP8-l00 UVIVIS apectrophotomfoter

Absorptionsspektrum des tiafgekOhlten Oiamanten (41 et) mit hoher Auft~sung, aurgenommen auf ei"em Pye Unlearn Spa-l00 UVIVIS-Spektralphotometer Abs. Ahs. )3 t G7U. - 0.5 t 711-/0

7UI 310.1 - O.~

- 0.3

GR-I -0.2

-0.1 ULTRAVIOLET VISIBLE , , I I 2'11J 3DD GlJ) ?a)

Copyright (j) 1988, G. BOSSHART. SSEF Gem Testing Laboratory, Zurich, Switzerland

FigFig.. 66.. High-resolutionHigh-resolution absorptioabsorptionn spectrumspectrum ooff ththee refriger­refriger­ ateatedd DresdenDresden GreenGreen DiamonDiamondd recordedrecorded oonn a PyePye aatt 534534 (±2)(±2) nm.nm. A greengreen huehue correspondscorresponds ttoo thisthis UnicamUnicam SP8-100SP8-100 UVIVISUV/VIS spectrometespectrometerr aatt four-foldfour-fold wavelengtwavelengthh (after(after DIDINN 61646164 huhuee nono.. 22\/2).22 V^). TheThe humanhuman 1 gaigainn anandd slowslow wavelengthwavelength scanninscanningg anandd chartchart advanceadvance eye,eye, however,however, sensesensess ththee huehue no.no. 21 \/2,/2, i.e.i.e. a slighllyslightly speed.speed. OpticaOpticall pathpath lengtlengthh frofromm tabltablee toto culeculett 10.28810.288 bluish-green becausbecausee thethe absorptionabsorption inin ththee blubluee isis eveneven (±0.005)(±0.005) mm.mm. ClassicaClassicall absorptionabsorption behaviourbehaviour ofof anan lowelowerr thanthan inin ththee orangeorange portionportion.. DueDue ttoo ththee fairlyfairly weakweak irradiateirradiatedd typetype IIIIaa diamond.diamond. GGRR 1 absorptionabsorption iinn ththee redred andand orangorangee regionsregions (right(right halhalff ooff FigurFiguree 4)4),, ththee colourcolour saturatiosaturationn ooff ththee DresdenDresden Main spectral characteristics araree ththee bandsbands ofof ththee GRGR 1 GreenGreen isis relativelyrelatively moderate.moderate. AAss a resulresultt ooff thisthis,, virtuallyvirtually absorptioabsorptionn systemsystem (750(750 toto 535300 nmnm,, presenpresentt inin allall nono bodybody coloucolourr isis visiblvisiblee througthroughh ththee culeculett (Figure(Figure 3)3).. irradiateirradiatedd diamondsdiamonds)) andand ththee GGRR 2-2-88 systemsystem.. ThThee widewide ThisThis observationobservation waswas confirmeconfirmedd bbyy comparisoncomparison withwith absorptionabsorption banbandd betweebetweenn 444400 andand 250250 nnmm iiss characteris­characteris­ thethe DIDINN ColourColour AtlaAtlass chartscharts (Tab.(Tab. 1:1 : degreedegree ofof satura­satura­ tictic ooff irradiateirradiatedd typtypee HIIaa diamondsdiamonds,, thethe chemicallychemically tiotionn ofof thethe bodbodyy coloucolourr K onlonlyy aboutabout 0.0.55 units,units, i.ei.e.. veryvery nearlynearly purpuree formform ooff naturalnatural anandd synthetisyntheticc diamonddiamond.. TheThe pale). absorptioabsorptionn lineline R 1111 occuroccurss onlyonly iinn typtypee IIaHa diamondsdiamonds pale). FortunatelFortunatelyy numerounumerouss vividlvividlyy greengreen internainternall reflectionsreflections (Davies(Davies,, 1977).1977). ThThee exceptionallexceptionallyy steesteepp anandd highhigh araree createcreatedd bbyy thethe interactioninteraction oftheof the exceptionalexceptional old-cutold-cut absorptioabsorptionn edgeedge ooff thethe DresdenDresden GreenGreen isis situatedsituated andand theGRthe GR 1 absorptionabsorption (Tab.(Tab . I:1 : degreedegree ofof saturationsaturation ofof immediatelyimmediately belobeloww 225225 nnmm iinn ththee short-waveshort-wave ultravioletultraviolet ththee reflectionreflection coloucolourr R arounaroundd 3 unitsunits,, i.e.i.e. a greegreenn ooff spectraspectrall region.region. mediumediumm saturation).saturation). ThThee absolutelyabsolutely lowestlowest absorbanceabsorbance ofof ththee DresdenDresden GreenGreen DiamonDiamondd iinn ththee regionregion ooff thethe spectraspectrall colourcolourss (visible(visible This reflection colour has made the Dresden Green into the electromagneticelectromagnetic waveswaves betweenbetween 700700 toto 400400 nmnm)) isis foundfound famous diamond admired forfor centuries. J. Gemm., 1989, 21, 6 359

The absorption diagram of the Green Diamond of negotiation with the director of the Green Vaults, Dr Dresden in the ultra-violet and visible portions J. Menzhausen, that the Dresden Green Diamond (Figure 6) now represents one of the first if not the should be removed from its mounting and weighed first published absorption spectrum for a naturally precisely, for the literature (Bauer, 1896, De Beers, green, cut diamond (thus being body-coloured) 1983, etc.) which until now contains the most which had been missed by Orlov (1977) and Collins incredible weight figures (cf. Table 1). Regrettably (1982) so far. After the author had already measured no permission could be procured for taking the other bluish-green old-cut brilliants of natural diamond out of its setting. At that point, the author coloration identified as type IaA diamonds (con­ unfortunately did not know that the girdle projects taining considerable amounts of nitrogen, mainly as over the top edge of the bezel on almost half of its pairs named A), it came as a great surprise in the circumference. Green Vaults when it became evident that the In order to be able to check the weight figure of Dresden Green unambiguously belonged to the 41 ct cited in most instances, two approaches of rarer, almost nitrogen-free type Ha. This observa­ weight estimation were chosen: tion was clearly confirmed by the absence of - the weight determination of the diamond in the absorption bands below 1600 cm"1 and above 2650 bezel setting did not permit a satisfactory cm"1 in the recorded mid-infrared transmission approximation in spite of the precise measure­ diagram. Artificially coloured diamonds of type Ha ment of the metal parts because their fineness hitherto encountered displayed indeed a blue colour was not known; but almost identical absorption spectra to that of the - calculation by means of the factor for the Green Diamond. conversion of dimensions into weight of a loose Virtually all diamonds showing a non-fluorescent pear-shaped old-cut brilliant of no less than green colour component owe this to the 13 ct proved unsuccessful because the propor­ influence of natural or artificial high-energy radia­ tions deviated too strongly from those of the tion. In both cases it generates defects in the carbon Dresden Green. lattice of diamond, the so-called vacancies, them­ Based on data gathered in the laboratory, the selves causing the same kind of selective light author reached the conclusion that a conversion absorption in all four known types of diamond (la, factor of 0.0065 would be the most supportable. lb, IIa, IIb), i.e. in the first place the GR 1 (General Calculation with this factor resulted in a weight of Radiation) absorption system presented in Figure 6. 41.1 ct and thus confirmed Menzhausen's value At the beginning of this century, W. Crookes (1987a). If the accurate weight differed, it would be executed the first intentional irradiations of dia­ slightly inferior (using the factor of 0.0064, near mond by applying radium salts. The green colora­ 40.5 ct). tion of diamonds can therefore only be accepted, for Diamonds of type IIa reveal a clear tendency to be the intended research study, as guaranteed natural if sizeable as well as nearly to completely colourless they spent the last one hundred years under credible (Collins, 1982, translator's footnote p. 164) if not supervision (e.g. in a museum) as stones known to irradiated like the Dresden Green. always have been green. Considering that industrial routine irradiation of diamond had already begun Examination of the Cut by approximately 1950, it must be attributed to The Green Diamond of Dresden was cut more fortunate circumstances that this can be proved for the Dresden Green even for its absence from than 240 years ago. Whoever examines this historic Dresden. cut will be astonished by the quality of its sym­ - firstly, the colour of the diamond had been metry, polish and proportions: described as pale green (Bauer, 1896) long according to prevailing grading regulations before the stone was stored away on the (CIBJO Rules 1986), the quality would have to be Königstein, a colour it still shows; classified as good or even very good. The table - secondly, the diamond retained several small facet of a diamond of 41 ct although being and shallow fissures with diffuse green specks expansive is optically plane. The common cor­ (Figure 7 and Table 1) encountered so far only ners of joining neighbour facets are perfectly as products of natural radiation emanating pointed. Facets of one kind have an identical size from radioactive groundwaters. and are not distorted. Table and culet are exactly Undoubtedly, however, these few irradiation spots concentric. The outline is pleasingly rounded and do not account for the homogeneous green colora­ symmetrical. The quality of this cut cannot easily tion of the Dresden Green. A natural body colour be rivalled by more recent old-cuts. And to beat it must be present. all, this remarkably cut diamond exhibits a Weight Estimation unique series of ratios of length to width, etc., in The author pointed out in the early stages of whole numbers (cf. Table 1). 360 J.Gemm.,1989,21,6

pressure only. In that manner neither the diamond nor the lead could heat up over a certain critical temperature. Without cutters of the past centuries having realized it, green diamonds were protected by the 'thermostat effect' of the lead/tin alloy. Pb/Sn solders melt at low temperatures, varying with composition (CRC 1978): Pb70/Sn30 at 255°C maximum Pb60/Sn40 at 238°C standard Pb40/Sn60 at 190°C minimum The green radiation colours of diamonds are sensi­ tive to heat, without exception. Hänni (1987 and 1988) checked this fact on an experimental basis on a naturally green-skinned diamond crystal and on an artificially greened brilliant. Many a diamond cutter of today involuntarily has had this experience with his own cutting goods (and many a diamond setter also during his jewellery work). The discoloration of green diamonds resulting from overheating is a continuous process of healing up the GR 1-8 radiation damage in the crystal lattice. This fading process starts already at 500°C, e.g. when diamonds are brought to red-heat which is performed easily on a modern 3000 rpm lap. In type la diamonds the discoloration of green comes to an end at about 800°C (Woods and Collins, 1986), in type Ha at higher temperatures (Davies, 1977). The process takes place quicker the higher the effective heat is. In general, uncontrolled annealing leads to unpleasant brown colour changes of incor- Fig. 7. Shallow fissure in one of the upper girdle facets showing rectable stability. diffuse green spots on the fissure walls, very probably Thanks to the thermostat reaction of the lead dop generated by radioactive waters having circulated on the after the ancient cutting technique, the discolora­ diamond deposit. Gold bezel (top) and silver bezel (bottom) visible below the fissure. Dark-field illumina­ tion of the Dresden Green could therefore not start tion. Length of longer fissure approx. 0.4mm. at all. Thus, if a larger number of historical green old-cut diamonds is unknown world-wide, this can only mean that these body-coloured diamonds The question shall be admissible whether such a are extremely rare, much rarer than the relatively perfection of cut was conceivable already in the abundant green-skinned rough diamond crystals. early eighteenth century. Tillander (1988) considers The latter lose their surface and sub-surface colora­ this possible if the diamond had been cut in tion entirely during cutting most of the time. London, and Guichon (1988) as well if a top cutter Occasionally however, individual green specks sur­ executed the opus. In those times already a lap vive the cutting process, more frequently on rem­ (scaife) of porous cast iron was employed. Yet it did nants of crystal faces ('naturals') than in natural not turn at 3000 but at less than 1000 rpm. The fissures, e.g. like^ those in the Dresden Green diamond was almost completely coated with lead, (Figure 7). The causes of this rarity of green body and the lead dop was mounted on a thin and flexible coloration will be pursued in the planned study. copper stick for easy adjustment of the facet angles Two further consequences of the low melting in relation to the grinding wheel. Because also less point of the lead dop are noteworthy: oil than boart was applied the cut remained 'cold' no burn marks can be observed on old-cuts after but took months for a large facet to be completed the lead dop technique was applied. As the author (Guichon, 1988). pointed out earlier, these surface corrosion marks develop only at 600°C (Hänni and Bosshart, Conclusions 1987). This temperature can be exceeded easily The secret why a diamond of this size possesses with modern cutting techniques. According to such an outstanding cut and still displays its original what has been said so far, the production of burn coloration is, that it was cut slowly and with little marks under the prongs of the mechanical dop of J. Gemm., 1989,21,6 361

today forcibly involves the destruction of green Appreciation body and skin-colours of diamond too; The author wishes to express his satisfaction the Green Diamond of Dresden cannot have concerning the availability of such a unique gem- exceeded the temperature of 260°C when it was stone as the Dresden Green for investigation, across cut more than 240 years ago. This means that the all borders. The successful outcome of the 'Dresden absorption band at 594 nm (in Figure 6 present in Green Project' creates the hope that in future an extremely weak intensity) cannot be an artefact increasing number of projects of particular scientific or caused by elevated cutting temperatures but cultural significance could be realized between East represents a natural property of the Dresden and West. Green. The absorption band at 594 nm only develops above 275°C (Woods and Collins, 1986) Acknowledgements while the line at 667 nm is destroyed above First of all to Dr J. Menzhausën, Director of the 430°C (Davies, 1977). Hence it follows that the Green Vaults, who deserves thanks for his readiness Dresden Green experienced a temperature of not to have the famous gemstone analysed and for his more than 350 (±80)°C in the earth's crust. endeavours in obtaining permission from the Ministry of Culture of the German Democratic Republic as well as Dr W Quellmalz of the Research Department of the State Museum of Mineralogy Summary and Geology at Dresden who supported and advised It can be stated that the Dresden Green Diamond: Dr Menzhausën on scientific and technical issues. 1. belongs to the rare and chemically pure type IIa Many thanks are owed to Mrs C. Wendt, restorer, and as such is typically big and free of macrosco­ and all her colleagues of the Green Vaults, the State pic inclusions; Museum of Mineralogy and Geology and the cus­ 2. possesses internal strain of normal strength toms and security services who assisted in the ('Tatami' type); completion of the investigation. 3. as an historical old-cut brilliant exhibits an Without the spirited response of Dr K. Herzog extraordinarily good cutting quality and note­ and Mrs R. Lunkwitz of the Physical Chemistry worthy proportions; Department of the Technical University at Dresden 4. was cut at slow speed, with little pressure and, in supplying an infrared spectrophotometer and mounted in a lead dop, at less than 260°C and technical know-how, evidence of the diamond type then was carefully set; could not have been secured completely. Kind 5. is damaged along the girdle (its purity and thanks are expressed to both as well as to their girdle theoretically being improvable by a pro­ superior, Prof. Dr E. Steger. fessional repolish); The author is indebted to his brother, Robert 6. very nearly weighs 4let; Bosshart, for assistance with the transportation of 7. should be weighed at least to the hundredth of the instruments and during the analysis, but fore­ the carat and be set anew; most for his valuable photographic documentation 8. experienced a moderate irradiation by radio­ of the Dresden Green Diamond and the working active ground-waters; scenes (e.g. Figures 1 to 5) under pressure of time. 9. does not show residual radioactivity; For microscopical examination and photomicro­ 10. reveals a non-fluorescent bluish-green colour graphy (Figure 7), the author was provided with a hue and a weak saturation (due to 8); Maxilab-Reichert Sierra StarZoom stereomicro- 11. evinces a rare heat-sensitive body colour (due to scope by Messrs R. E. Kane and S. F McClure of 1 and 8); the Gemological Institute of America, Los Angeles. 12. displays a brilliant reflection colour (thanks to 3 He is thankful to both colleagues for their collabora­ and 8); tion prior to and during the period of research. 13. was heated in the earth's crust to about 350°C; It is also recognized with thanks that the Board of 14. has retained its green coloration (owing to 4 and Councillors of the SSEF Foundation participated in 13) but could lose it on the occasion of a the necessary time exemption of the author and in repolishing operation on a rapid lap; the expenses for the project. In addition, the 15. however, endured multiple deep freezing in a mastering of the workload at the SSEF Laboratory nitrogen gas atmosphere without any problems; in Zurich by the author's colleagues, Mrs M. 16. differs little in absorption behaviour from type Fritsche and Dr H. A. Hänni, is gratefully acknow­ Ha diamonds artificially coloured blue; and ledged. The article benefited from the photography 17. will not reveal its place of origin in the near of the absorption spectrum (Figure 6) and from future, based on the inclusions present and on technical discussions with Dr Hänni. the criteria enumerated above. Special thanks go to Mr A. Guichon, a diamond 363622 JJ.. Gemm.Gemm.,, 19891989,21,6, 21, 6

cuttecutterr experienceexperiencedd iinn ololdd anandd neneww cuttincuttingg techtech­­ CopelandCopeland,, L.L.L. L.,, 19661966.. Diamonds…Famous,Diamonds . .. Famous, notablenotable and unique. niquesniques,, anandd ttoo MMrr DD.. RouxRoux,, a skilleskilledd gemstongemstonee GemologicaGemologicall InstitutInstitutee ooff AmericaAmerica,, LoLoss AngelesAngeles,, 1s1stt ed.ed.,, settesetterr whwhoo informeinformedd ththee authoauthorr abouaboutt ththee 'Genev'Genevaa 24-524-5,, 28-28-99 anandd 47-847 -8.. CRCRCC HandbooHandbookk ooff ChemistrChemistryy anandd PhysicsPhysics,, 19781978.. CRCRCC PresPresss bezelbezel'' settinsettingg ooff ththee DresdeDresdenn GreenGreen.. ThThee authoauthorr iiss Inc.Inc.,, WesWestt PalPalmm BeachBeach,, FloridaFlorida,, 59t59thh ed.ed.,, F-173F-173.. alsalsoo obligeobligedd ttoo DDrr HH.. UU.. PfistePfisterr ooff th thee StatStatee ArchiveArchivess Davies, G., G., 1977. 1977. The The Optical Optical Properties Properties of Diamond. of Diamond. Chemistry Chern­ aatt ththee UniversitUniversityy ooff ZuricZurichh foforr hihiss knowledgeablknowledgeablee and PhysicsistryandPhysicsofCarbon. of Carbon. 13, 1-143. 13,1-143. transcriptiotranscriptionn ooff th thee InventorInventoryy entriesentries.. DDee BeersBeers,, 19831983.. Notable Diamonds of thethe World. DiamonDiamondd Promotion Service, New York, 14,20,60,69. Furthermore the author appreciates the assist­ Promotion Service, New York, 14, 20, 60, 69. Furthermore the author appreciates the assist­ Guichon, A., A., diamond diamond cutting cutting studio, studio, Zurich, Zurich, personal personal communications, com­ ancancee ooff severaseverall friendfriendss iinn developindevelopingg anandd outfittingoutfitting 1987munications, and 1988. 1987 and 1988. ththee coolincoolingg celcelll anandd alsalsoo ththee helhelpp bbyy DDrr MM.. Hänni,Hanni, H.A., H.A., SSEF SSEF Laboratory, Laboratory, Zurich, Zurich, personal personal communications, communica­ RosenfeldRosenfeld,, a solid-statsolid-statee physicisphysicistt iinn cryogenicscryogenics,, iinn 1987tions, and 1988. 1987 and 1988. HänniHanni,, H.A.H.A.,, BossharBosshartt G.G.,, 19871987.. DamagDamagee ttoo cucutt DiamondsDiamonds.J.. J. establishinestablishingg ththee evidencevidencee ooff innocuousnesinnocuousnesss iinn ththee Gemm, 2020,, I 66,, 339-43339-43.. Swiss Watch & Jewelry Journal, 22,, refrigeratiorefrigerationn foforr ththee DresdeDresdenn GreenGreen.. 383-6383-6,, Diamani, 2929,, 305305,, 21-621-6.. MrMrss JJ.. Müller-CollinMuller-Collinss ooff HorgeHorgenn deservedeservess warmwarm­­ HoferHofer,, S.C.S.c.,, MansonManson,, D.V.D.V.,, 19811981.. CryogenicsCryogenics,, aann aiaidd ttoo esestt thankthankss foforr carefucarefull reviewinreviewingg anandd proof-readingproof-reading gemstongemstonee testingtesting.. Gems & Gemology, 1717,, 33,, 143-9143-9.. MenzhausenMenzhausen,, J.J.,, 1987a1987a.. EinführungEinfuhrung inin das GrüneGrune GewölbeGewiilbe (i(inn ooff ththee translationtranslation.. GermanGerman,, IntroductioIntroductionn ttoo ththee GreeGreenn Vaults)Vaults).. StaatlicheStaatliche I alsalsoo recorrecordd mmyy thankthankss ttoo mmyy BritisBritishh friendsfriends,, DrDr KunstsammlungeKunstsammlungenn DresdenDresden,, 13t13thh ed.ed.,, 121200 pp.. AA.. TT.. CollinsCollins,, EE.. AA.. JobbinJobbinss anandd KK.. ScarrattScarratt,, forfor Menzhausen, J., ]., Green Green Vaults, Vaults, Dresden, Dresden, personal personal communications, communica­ theitheirr scientifiscientificc anandd editoriaeditoriall adviceadvice.. 1987btions, and 1988.1987b and 1988. OrlovOrlov,, Y.L.Y.L.,, 19771977.. The Mineralogy of Diamond. JohJohnn WileyWiley,, LondonLondon,, 111166 anandd 124124.. PfisterPfister,, H.U.H. U.,, UniversitUniversityy ooff ZurichZurich,, transcriptiotranscriptionn ooff registrationregistration nosnos.. 5500 anandd 5511 iinn ththee GreeGreenn VaultVaultss InventoryInventory;, 2 DecemberDecember 19881988.. ReferenceReferencess RöschRosch,, S.S.,, 19691969.. FarbmessungeFarbmessungenn aamm DiamanteDiamantenn (i(inn German,German, Arnold, U., U., 1988. 1988. Green Green Vaults, Vaults, Dresden, Dresden, personal personal communication, communica­ ColouColourr MeasurementMeasurementss ooff Diamond)Diamond),, 1I.. TeilTeiI.Z.Dt.. Z. Dt. Gemmol. 25 Nov.tion, 1988. 25 Nov. 1988. Ges., 1818,3,, 3, 126-40126-40.. BauerBauer,, M.M.,, 18961896.. Edelsteinkunde. ChrChr.. HerrnHerm.. TauchnitTauchnitzz VerlagVerlag,, Rosenfeld, M., M., Bosshart, Bosshart, G., G.,Zurich, Zurich, evidence evidence of innocuousness, of innocuous­ LeipzigLeipzig,, 1s1stt ed.ed.,, 156-156-77 anand287.d 287. PreciousPreciousSlOnes, Stones, 1968,1968, DoverDover 17 Decemberness, 17 December1987. 1987. PublicationsPublications,, NeNeww YorYorkk (Republicatio(Republicationn ooff Precious Stones,Stones, ScarrattScarratt,, K.K.,, 19791979.. InvestigatinInvestigatingg ththee visiblvisiblee spectrspectraa ooff colouredcoloured 19041904,, ChCh.. GriffinGriffin,, LondonLondon,, firsfirstt EnglisEnglishh edition)edition).. diamondsdiamonds.J.. J. Gemm. 16,7,433-47.16, 7, 433-47. BiesalskiBiesa1ski,, E.E.,, 19571957.. Pflanzenfarbenatlas DIN 6164 (i(inn German,German, TillanderTillander,, H.H.,, HelsinkiHelsinki,, personapersonall communicationcommunication,, 2233 NovemberNovember PlanPlantt ColouColourr Atlas)Atlas).. Musterschmidt-VerlagMusterschmidt-Verlag,, Gottingen.Göttingen. 19881988.. BosshartBosshart,, G.G.,, 19891989.. GreeGreenn anandd blubluee DiamondDiamondss (i(inn preparation)preparation).. WatzdorfWatzdorf,, EE.. vonvon,, 19621962.JohannMelchiorDinglinger.. Johann Melchior Dinglinger. Gebr.Gebr. MannMann CIBJCIBJOO (International(International ConfederationConfederation ofof JewelryJewelry,, Silverware,Silverware, VerlagVerlag,, Berlin.Berlin. DiamondsDiamonds,, PearlsPearls,, andand Gemstones),Gemstones), 1986,1986, Rules forfor the Woods, G.S.,G.S., Collins, Collins, A.T., A.T., 1986. 1986. New New developments developments in spectroscopic in spec­ Diamond Trade. CIBJOCIBJO,, DeDenn HaagHaag,, neneww edition.edition. methodstroscopic for detecting methods artificially for detecting coloured artificially diamonds. coloured dia­ CollinsCollins,, A.T.A. T.,, 1982.1982. ColourColour CentresCentres inin DiamondDiamond.. JJ.. Gemm.,Gernm., 1818,, J. Gemm.,monds.J. 20, 2, Gemm., 75-82. 20, 2, 75-82. 1I,, 37-7537-75.. FarbzentreFarbzentrenn inin DiamantenDiamanten,, Z. Dt. Gemmol. Ges.,Ges., 1982,31,3,157-921982, 31, 3, 157-92 (German(German translatiotranslationn bbyy GG.. Bosshart).Bosshart). [[ManuscriptManuscript receivedreceived 1818 February, February, 1989.]1989.] J. Gemm., 1989, 21, 6 363

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j 364364 J.J. Gemm.,Gemm., 1989,21,6 1989, 21, 6

'Aqu~quaa Aura'Aura' enhancedenhanced quartz quartz specimens specimens

Robert C. Kammerling andJohnand John I. KoivulaKoivula

GemologicalGemological InstituteInstitute ofof America,America, SantaSanta Monica,Monica, Calif.Calif. 90404,90404, USAUSA..

AbstractAbstract AccordingAccording toto a smallsmall slipslip ofof promotionalpromotional litera­litera­ Singly andand doubly terminated euhedraleuhedral quartzquartz crys­crystals tureture obtainedobtained atat thethe PasadenaPasadena Show,Show, 'Aqua'Aqua Aura'Aura' tals andand crystalcrystal clustersclusters withwith a coatingcoating producinproducingg aann specimensspecimens areare 'Natural'Natural quartzquartz crystalscrystals coatedcoated withwith apparentapparent blueblue colourcolour andand strongstrong iridescenceiridescence areare beingbeing purepure gold:gold'. FollowingFollowing isis somesome additionaladditional texttext pro­pro­ soldsold underunder thethe tradetrade namename 'Aqu'Aquaa Aura:Aura'. TheThe authorsauthors videdvided withwith ththee crystalscrystals thatthat relaterelate ttoo thethe coatingcoating report on theirtheir examinationexamination of a specimen which con­confirmedprocesprocess s usedused:: 'Quartz'Quartz crystalscrystals areare naturallnaturallyy sur­sur­ firmedthat thethat coating the coating consists consists of gold. of gold. rounderoundedd bbyy anan electricalelectrical charge.charge. AquaAqua AuraAura isis IntroductionIntroduction createdcreated bbyy allowingallowing purpuree goldgold moleculesmolecules toto adhereadhere InIn thethe FallFall ofof 19881988 oneone ofof thethe authorsauthors (RCK)(RCK) waswas toto thatthat charge.charge. TheThe extremelyextremely thinthin goldgold coatingcoating shownshown anan interestinginteresting quartzquartz specimenspecimen byby Mr.Mr. PeterPeter breakbreakss lightlight intointo itsits spectralspectral colours,colours, causingcausing thethe FlusserFlusser ofof OverlandOverland GemsGems inin LosLos Angeles,Angeles, Califor­Califor­ beautifubeautifull colourscolours ofof AquAquaa Aura.'Aura.' WitWithh respecrespectt toto nia.nia. TheThe crystalcrystal waswas singly-terminated,singly-terminated, weighedweighed durability,durability, ththee promotionalpromotional piecepiece statesstates thatthat 'Aqua'Aqua 47.5047.50 ct.ct. andand measuredmeasured 5252 millimetresmillimetres inin length.length. ItIt AuraAura requirerequiress nono specialspecial carecare toto keekeepp itsits beauty.beauty. hadhad anan unusualunusual lightlight blueblue toto greenishgreenish blubluee bodybody TheThe goldgold coatingcoating cannotcannot bbee rubberubbedd oror scrapedscraped off:off! colourcolour (Figure(Figure la)la) andand strongstrong iridescentiridescent colourscolours onon allall surfacessurfaces (Figure(Figure 1lb)b); ; ThisThis authorauthor was informedinformed GemmologicalGemmological examinationexamination thatthat thethe specimenspecimen hadhad beebeenn obtainedobtained fromfrom ththee fIrmfirm TheThe examinationexamination begabegann withwith ththee testintestingg ofof thethe BobBob JacksonJackson MineralsMinerals inin Renton,Renton, Washington,Washington, andand quartzquartz crystalcrystal toto determinedetermine itsits gemmologicalgemmological prop­prop­ waswas beingbeing marketedmarketed asas 'Aqua'Aqua Aura'Aura:. TheThe authorsauthors erties.erties. TheThe crystalcrystal hadhad a colourcolour thathatt varievariedd fromfrom subsequentlysubsequently sawsaw additionaladditional specimensspecimens atat thethe greenish-bluegreenish-blue ttoo blue,blue, witwithh overlyingoverlying iridescentiridescent annuaannuall PasadenaPasadena GemGem andand MineralMineral ShowShow inin colourscolours ofof violet,violet, blue,blue, greengreen andand yellow.yellow. OfOf thethe Pasadena,Pasadena, California,California, andand Dr.Dr. EmmanuelEmmanuel FritschFritsch iridesceniridescentt colours,colours, ththee violetviolet waswas mosmostt prominent.prominent. ofof GIA'sGIA's ResearchResearch DepartmenDepartmentt laterlater providedprovided a Overall,Overall, ththee crystalcrystal hahadd a highighh degreedegree ofof trans­trans­ crystalcrystal clustercluster ofof thisthis coatedcoated quartzquartz givegivenn toto himhim parency.parency. AAss thethe crystalcrystal facesfaces ofof ththee specimenspecimen werewere directlydirectly bbyy BobBob JacksonJackson forfor visuavisuall examinationexamination well-formedwell-formed withwith reasonablreasonablyy goodgood surfacesurface lustre,lustre, (Figure(Figure 2)2).. flatflat facetfacet refractivrefractivee indicesindices readingreadingss werweree takentaken

Figs.Figs, lala &.& b.b. 'Aqua'Aqua Aura'Aura' coatedcoated quartzquartz crystalcrystal (GIA(GIA CollectionCollection NoNo.. 16667)16667) showingshowing (left)(left) thethe blueblue colourcolour (right)(right) thethe iridescentiridescent colourscolours providedprovided byby ththee coating.coating. ObliqueOblique fibrefibre opticoptic illumination.illumination. Photos by William Videto.

© CopyrightCopyright thethe GemmologicalGemmological AssociationAssociation ISSN:ISSN: 0022-12520022-1252 J.Gemm.,1989,21,6 365

Fig. 2 (centre). 'Aqua Aura' quartz crystal cluster. Oblique fibre optic illumination. Photo by William Videto.

Fig. 3 (top, left). 'Aqua Aura' coated quartz crystal showing areas devoid of the coating and colour concentrated along the edge of the crystal face. 40x. Photo by John I. Koivula.

Fig. 4 (top, right). Surface pits on an 'Aqua Aura' quartz crystal in which little or no coating was observed. 30x. Photo by John I. Koivula.

Fig. 5 (right). Iridescent surface layer on an 'Aqua Aura' quartz crystal. 10x. Photo by John I. Koivula. 366 J. Gemm., 1989,21,6

using a GIA GEM Instruments Duplex II refracto- (Ti02) in the quartz crystal or more probably from meter and near-monochromatic light. Somewhat titanium in solid solution, because it is well known vague readings of 1.54-1.55 were obtained. In a that titanium is one of the secondary elements field of polarized light a typical doubly refractive commonly found as a solid solution constituent in reaction was noted. natural quartz (Frondel, 1962). The other major The specimen was also examined for its reaction element detected, gold, supports the information to ultraviolet radiation and proved to be inert to from the vendor that the coating used is pure gold. both long- and short-wavelengths. No visible Dr. Fritsch also noted that, when tested for elec­ absorption features were noted when the crystal trical conductivity on a conductometer, in some was examined with both diffraction-grating and areas the gold coating showed excellent conduc­ prism type hand held spectroscopes, using both tivity. transmission and external reflection lighting methods. Specific gravity was determined by immersing Table 1: Summary of gemmological properties the crystal in a mixture of methylene iodide and benzyl benzoate calibrated to 2.67. When placed in Colour: Greenish-blue to blue this liquid the crystal floated very slowly - at essentially the same rate as an untreated rock Iridescent colours: Violet, blue, green and crystal quartz. Specific gravity was thus estimated yellow; violet most at 2.66. prominent Under magnification the coating revealed a number of interesting features. First, it appeared Diaphaneity: Transparent to vary in thickness on some crystal faces, with some small areas showing no coating at all (Figure Refractive indices: o-1.54; e-1.55 3). It also seemed not to have deposited as well in surface pits as it had on flat surfaces (Figure 4). Polariscope reaction: Doubly refractive The colour also looked to be concentrated near crystal edges (Figures 3 and 4) and appeared as if it UV fluorescence may have been deposited directionally. Long-wave: inert Short-wave: inert Durability testing A number of additional tests were performed to Absorption spectrum: none determine the relative durability of the coating. A hardness pencil of Mohs hardness 6 failed to Specific gravity: 2.66 (heavy liquid scratch the crystal or produce any visible mark on method) the coating, while one of Mohs hardness 7 pro­ duced a scratch. No visible reaction was noted Hardness: 6V2-7 when the surface was tested with a thermal reac­ tion tester heated to a red heat (approximately 800 Reaction to heat: None observed to 1000- degrees Centigrade). The crystal was then placed 1100 degrees C. on an electrically-activated 'KanthaP bridge and heated to a temperature of approximately 1000- Reaction to acetone: None 1100 degrees Centigrade (gold melts at 1064 de­ grees Centigrade). This also appeared to have no effect on the coating. Finally, one crystal face was Discussion rubbed vigorously with a cotton swab dipped in The blue colour shown by 'Aqua Aura' quartz is acetone. No discoloration appeared on the swab not an interference colour. Gold in thin film is and no visible effect was noted on the crystal face. bluish-green in transmitted light. Thus the green to blue colour exhibited by 'Aqua Aura' quartz is Chemical analysis the true absorption-caused colour of gold (Nassau, The crystal was next examined by means of 1983). energy dispersive X-ray fluorescence (ED-XRF) to In addition to the thin film effects observed determine its elemental characteristics. The major internally as inclusions in some gems (Koivula, elements detected were silicon, gold and titanium. 1980), thin film coatings, similar to the iridescent The silicon was almost certainly from the quartz surfaces (Figure 5) shown by these artificially itself. It is believed that the titanium detected may gold-coated 'Aqua Aura' quartz crystals, are known have been from sub-microscopic rutile inclusions to occur in nature. The common oil slick on water J. Gemm., 1989,21,6 367 is probably the best single example (Ribbe, 1972) also appear to be accurate. At this point in time we but some types of sun-oxidised glass, certain have only seen single quartz crystals and crystal minerals such as cuprite, and the gems faceted clusters given the 'Aqua Aura' treatment. But, from them, will also often show iridescent, metal­ knowing the history of other gemstone treatments, lic-appearing superficial thin films. The iridesc­ can faceted 'Aqua Aura' gems be far off? ence colours superimposed on the surface of 'Aqua Aura' quartz are related to the thickness of the gold Acknowledgements film, probably of the same order of magnitude as The authors would like to thank Mr Peter the visible wavelength. Flusser of Overland Gems, Los Angeles, Califor­ If we think of the already existing technology in nia, for providing them with the first specimen relation to thin film applications of elemental gold, examined. Dr Emmanuel Fritsch of the Research then the appearance of 'Aqua Aura' in the gem and Department, Gemological Institute of America, mineral trade is not too surprising. Many of today's Santa Monica, California and Mr John Armstrong modern synthetics came to gemmology from other of the California Institute of Technology, Pasadena, fields of science such as laser research and the California performed the ED-XRF analysis; Dr computer industry. Now, as an apparent spin-off Fritsch also provided the crystal cluster specimen from the thin film gold-coating technology that and gave the authors some excellent advice for gives us the sun visors on astronauts' helmets and improvement of the manuscript. Thanks also to the vacuum deposited conductive coatings for Mr William Videto, Residence Colored Stones scanning electron microscopy, we have 'Aqua instructor, Gemological Institute of America, Santa Aura'. Monica, for providing the macrophotography.

Conclusion References Based on the examination of this 'Aqua Aura' Frondel, Clifford, 1962. The system of mineralogy, Vol. 3, 7th coated quartz crystal (GIA Collection No. 16667) edn. John Wiley & Sons, Inc., New York. as summarised in Table 1, it appears that the Koivula, John I., 1980. Thin films: elusive beauty in the world of inclusions. Gems & Gemology, 16, 9, 326-30. coating does not affect the normal quartz prop­ Nassau, Kurt, 1983. The physics and chemistry of color. John erties. The vendor's claim that the coating is 'pure Wiley & Sons, Inc., New York. 166-7. gold' is substantiated through energy dispersive Ribbe, Paul H., 1972. Interference colours in oil slicks and X-ray fluorescence testing. Furthermore, in view feldspars. The Mineralogical Record, 3, 1, 18-22. of the rigorous durability testing, statements relat­ ing to the relatively durable nature of the coating [Manuscript received 3 November 1988.] 368368 J.J. Gemm.,Gemm., 1989,21,61989, 21, 6

MethodsMethods forfor thethe distinctiondistinction ofof naturalnatural andand syntheticsynthetic citrinecitrine andand prasioliteprasiolite

Dr Karl SchmetzerSchmetzer

InstituteInstitute ofof MineralogyMineralogy andand Petrography,Petrography, UniversityUniversity ofof Heidelberg,Heidelberg, WestWest GermanyGermany

AbstractAbstract distinctiondistinction ofof naturalnatural versusversus syntheticsynthetic c!trIne.citrine. MosMostt DifferentDifferent typestypes ofof naturalnatural andand syntheticsynthetic citrinecitrine araree naturalnatural citrinescitrines usedused inin ththee tradetrade areare heat-treatedheat-treated naturalnatural characterized by aa combination ofof absorptionabsorption spectro­spectroscopyamethysts.amethysts . However,However, non-artificially-irradiated,non-artificially-irradiated, nonnon­- scopyin the in visiblethe visible and ultravioletand ultraviolet range range with withmicroscopic micro­ heat-treatedheat-treated oror heat-treateheat-treatedd asas wellwell asas irradiatedirradiated andand scopic investigationsinvestigations ofof structuralstructural propertiepropertiess suchsuch aass possiblypossibly heat-treatedheat-treated naturalnatural quartzquartz isis alsoalso found.found. MosMostt twinning,twinning, growthgrowth structures,structures, coloucolourr zoningzoning asas wellwell aass syntheticsynthetic citrinescitrines ofof thethe tradetrade areare differentdifferent typestypes ooff orientated channel-like inclusions or orientated striations.stria­ Fe-bearingFe-bearin g asas wellwell asas Fe-Fe- andand Co-containingCo-containing quartzquartz tions. crystals,crystals, whichwhich areare growngrown hydrothermallyhydrothermally fromfrom K2CO3r - BothBoth methodmethodss revealreveal a numbernumber ofof typicaltypical featuresfeatures bearingbearing solutionssolutions withwith oror withoutwithout additionaladditional oxidizersoxidizers.. which indicate artificialartifIcial irradiation and/orand/or heatheat treatment.treat­ TraceTrac e elementelement analysesanalyses ofof syntheticsynthetic citrinecitrine cancan indicateindicate ment. TheThe colourcolour ofof naturalnatural andand syntheticsynthetic citrinecitrine isis growthgrowth mediamedia andand oxidizersoxidizers usedused inin thethe workingworking solu­solution. causedcaused byby tracestraces ofof ironiron and/orand/or cobalt,cobalt, asas wellwell asas bbyy Ition. Introductio n radiation-induceradiation-inducedd colourcolour centres.centres. AccordingAccording toto colourcolour I Introduction causescauses andand treatmenttreatment histories,histories, naturalnatural andand syntheticsynthetic citrines are classified intointo different categories asas indi­indicated InIn thethe pastpast yearsyears greatgreat effortsefforts werewere mademade andand catedbelow: below: manymany investigationsinvestigations werewere undertakenundertaken forfor thethe char­char­ (a)(a) yellowyellow toto orange-brownorange-brown heat-treatedheat-treated naturalnatural citrinecitrine,, acterizationacterization ofof thethe propertiesproperties ofof naturalnatural andand synthe­synthe­ originallyoriginally amethyst:amethyst: Fe-containingFe-containing particles;particles; tictic amethystamethyst inin orderorder toto developdevelop practicablepracticable (b)(b) greengreen heat-treatedheat-treated naturalnatural prasioliteprasiolite,, originallyoriginally methodsmethods forfor thethe distinctiondistinction ofof naturalnatural andand syntheticsynthetic 22+ amethyst:amethyst: Fe-containingFe-containing particleparticless anandd Fe + (I(16);6); samples.samples. InIn thethe paperspapers publishedpublished soso farfar emphasisemphasis isis (c)(c) lightlight yellow,yellow, non-artificially-irradiated,non-artificially-irradiated, non-heat­non-heat- laidlaid onon infraredinfrared spectroscopyspectroscopy andand microscopymicroscopy asas thethe treatedtreated naturalnatural citrine;citrine; radiation-inducedradiation-induced colourcolour cen­centres; twotwo dominantdominant methodsmethods toto recognizrecognizee featuresfeatures usefuluseful tres; forfor diagnosticdiagnostic purposespurposes (e.g.(e.g. SchmetzerSchmetzer andand Bank,Bank, (d)(d) lightlight yellow,yellow, non-artifIcially-irradiated,non-artificially-irradiated, heat-treatedheat-treated 1980;1980; ZecchiniZecchini andand MerigollX,Mérigoux, 1980;1980; LindLind andand naturalnatural citrine:citrine: originallyoriginally morion:morion: radiation-inducedradiation-induced Schmetzer, 1982, 1983; Schneider and Dröschel, colourcolour centrescentres;; Schmetzer, 1982, 1983; Schneider and Droschel, 1983; Lind et al, 1983, 1985; Schmetzer, 1985, (e)(e) greenish-yellowgreenish-yellow artificially-irradiated,artificially-irradiated, non-heat­non-heat- 1983; Lind et ai., 1983, 1985; Schmetzer, 1985, treatedtreated naturalnatural citrine,citrine, originallyoriginally colourlesscolourless quartz:quartz: 1986;1986; LindLind andand Schmetzer,Schmetzer, 1985,1985, 1987;1987; Crowning­Crowning- radiation-inducedradiation-induced colourcolour centres;centres; shieldshield et ai.,al. 9 1986)1986).. AlthougAlthoughh iinn somsomee ooff ththee paperpaperss (f)(f) greenish-yellowgreenish-yellow artificially-irradiated,artificially-irradiated, heat-treatedheat-treated mentionedmentioned above,above, somesome hintshints areare givengiven whichwhich areare naturalnatural citrine,citrine, originallyoriginally colourlesscolourless quartz:quartz: radiation­radiation- usefuluseful forfor thethe distinctiondistinction ofof naturalnatural andand syntheticsynthetic inducedinduced colourcolour centres;centres; citrine,citrine, nono comprehensivecomprehensive publicationpublication existsexists whichwhich (g)(g) yellowyellow toto orange-brownorange-brown syntheticsynthetic citrine:citrine: FeFe­- enablesenables thethe practicalpractical gemmologistgemmologist toto decidedecide containingcontaining particlesparticles;; whether a yellow or brown quartz of unknown (h)(h) yellowyellow toto orange-brownorange-brown syntheticsynthetic citrine:citrine: FeFe­- whether a yellow or brown quartz of unknown 3+ originorigin isis a naturalnatural oror man-made,man-made, treatedtreated oror untreateduntreated containingcontaining particlesparticles andand Fe3+Fe (I(14);4); stone (cf. O'Donoghue, 1983). (i)(i) greengreen syntheticsynthetic prasiolite:prasiolite: Fe-containingFe-containing particlesparticles,, stone (cf. O'Donoghue, 1983). 3+ 22+ Fe3+Fe (14)(I4) andand Fe + (I(16);6); InIn thethe presentpresent publicatiopublicationn a combinationcombination ofof (j)(j) yellowyellow toto orange-brownorange-brown syntheticsynthetic citrine:citrine: FeFe­- absorptionabsorption spectroscopyspectroscopy inin thethe visiblevisible andand ultra­ultra­ 3+ containingcontaining particlesparticles andand Co3+Co (I(1 6));; violetviolet areasareas withwith microscopicmicroscopic investigationsinvestigations isis sug­sug­ (k)(k) greenish-yellowgreenish-yellow artificially-irradiated,artificially-irradiated, non-heat­non-heat- gestedgested asas a routineroutine methodmethod forfor a distinctiondistinction betweenbetween treatedtreated syntheticsynthetic citrine,citrine, originallyoriginally colourlesscolourless syntheticsynthetic naturalnatural andand syntheticsynthetic membersmembers ofof thethe quartzquartz familyfamily quartz:quartz: radiation-inducedradiation-induced colourcolour centres;centres; withwith yellow,yellow, greenish-yellow,greenish-yellow, green,green, orange-brownorange-brown (I)(l) greenish-yellowgreenish-yellow artificially-irradiated,artificially-irradiated, heat-treatedheat-treated or brown coloration. However, before describing syntheticsynthetic citrine,citrine, originallyoriginally colourlescolourlesss syntheticsynthetic quartz:quartz: or brown coloration. However, before describing radiation-inducedradiation-induced colourcolour centres.centres. thethe characteristiccharacteristic featuresfeatures ofof naturalnatural andand syntheticsynthetic A numbernumber ofof specifiCspecific propertiesproperties waswas foundfound whichwhich areare quartzquartz varieties,varieties, itit isis necessarynecessary toto givegive a shortshort reviewreview usefuluseful foforr thethe determinationdetermination ofof growthgrowth and/orand/or treatmenttreatment ofof thethe scientifICscientific literatureliterature dealingdealing withwith colourcolour andand historieshistories ofof samplessamples ofof unknownunknown originorigin andand forfor a colourcolour causescauses ofof naturalnatural citrinecitrine typestypes asas wellwell asas withwith J. Gemm., 1989,21,6 369 the production of synthetic yellow, yellowish-green, and Troup, 1966; Lehmann, 1967, 1971a, b; Wild, green, orange-brown and brown quartz. With the 1968; Lehmann and Bambauer, 1973; Stock and information given in the literature, most of the Lehmann, 1977; Neumann and Schmetzer, 1984a, properties of all different types of natural and b). The colour of heat-treated natural amethyst synthetic citrine, which are found in the gem trade, crystals, which turn green during the annealing can be understood. In addition, a short overview of process (the so-called prasiolite of the trade) is due the literature should help to avoid further confusion to interstitial Fe2+ on distorted octahedral sites, 2+ 2+ between the different types of natural and synthetic designated Fe (I6). The absorption band of Fe citrines described so far, as well as between different (I6) in quartz in the visible region is centred in the applications of closely related terms such as citrine, red area at about 13,500 cm-1 (approx. 741 nm), a honey quartz and greenish-yellow quartz for sam­ second broad absorption band is observed at 10,500 ples of identical origin or with similar growth and/or cm-1 (approx. 950 nm) in the near infrared treatment histories (cf. Nassau, 1977). (Lehmann, 1967; Lehmann and Bambauer, 1973; According to the personal opinion of the present Neumann and Schmetzer, 1984a,b). author, for practical reasons the terms natural citrine and synthetic citrine should be used for all II. 2 GREENISH-YELLOW, IRRADIATION-TREATED yellow, greenish-yellow, orange-brown and brown NATURAL QUARTZ (ORIGINALLY COLOURLESS OR members of the quartz group, as well as the terms LIGHT YELLOW) natural prasiolite and synthetic prasiolite for green Colourless natural quartz crystals of peculiar occurrences turn smoky or greenish-yellow by samples. The main argument for this suggestion is irradiation treatment with gamma rays. After subse­ that the determination of the exact colour-causing quent heat treatment of irradiated samples at lower trace element or colour-causing defect (colour cen­ temperatures (e.g. about 150 - 250°C), smoky- tre) is not practicable in the gem trade for each quartz may turn greenish-yellow or colourless. sample. However, a general decision of international Greenish-yellow quartz, which is produced by heat nomenclature commissions, e.g. a decision of the treatment of smoky quartz or directly without Commission on Gem Materials of the International annealing by gamma irradiation, becomes colour­ Mineralogical Association or a decision of the less again by heat treatment at higher temperatures CIBJO Commission, for the use of the term citrine (e.g. about 250 - 350°C). Two different descriptions are needed in order to clarify and avoid all possibili­ and interpretations of the absorption spectra of ties of misunderstanding and misinterpretation. irradiated greenish-yellow quartz and irradiated smoky quartz, which turned greenish-yellow after II Review of the literature dealing with yellow, subsequent heat-treatment, are found in the litera­ greenish-yellow, green, orange-brown or brown ture. quartz varieties The first group of authors measured absorption A general survey of natural and synthetic quartz spectra with two distinct maxima, one of them varieties, growth conditions and colour causes is -1 between 24,400 and 25,600 cm (410 and 390 nm), given by various authors; these papers are sug­ the second one between about 15,600 and 16,100 gested for additional reading (Gordienko et al., cm-1 (640 and 620 nm). Both absorption bands are 1969; Lehmann and Bambauer, 1973; Hutton, superimposed by an absorption in the ultraviolet 1974; Lehmann, 1978a, b; Balakirev et al, 1979; area, the low energy tail of which extends to the Elwell, 1979; Nassau, 1980; Balitsky, 1981; Sunaga- visible region (Samoilovich et al., 1969b; Bukanov wa, 1982). and Markova, 1969; Lehmann, 1971a, b; Lehmann II. 1 HEAT-TREATED NATURAL AMETHYST and Bambauer, 1973; Samoilovich et al., 1976; cf. Most yellow, yellowish-brown, orange-brown also the paper dealing with neutron irradiated and brown natural citrines of the trade are natural quartz by Maschmeyer and Lehmann, 1984). Most amethysts which were converted to citrine by heat characteristic for all these publications is the de­ treatment at temperatures between approximately scription of an absorption maximum in the 24,400 -1 400 and 600°C. The absorption spectrum of this to 25,600 cm area (410 to 390 nm), the position of type of citrine consists of an increasing absorption which is distinctly shifted to the short wavelength from the red area to the violet end of the visible region compared with the position of the ordinary region, which is due to an absorption band centred maximum of the smoky colour centre in quartz. The in the ultraviolet area and extending into the visible maximum of this Al-related colour centre is found -1 range with its low energy tail. According to EPR- at approximately 23,400 to 22,200 cm (427 to 450 investigations, this absorption is caused by small nm). iron-containing particles, presumbly Fe203 precipi­ The second group of papers dealing with irradia­ tates, which are submicroscopically dispersed in the tion-induced colour of greenish-yellow quartz de­ host crystal (Lehmann and Moore, 1966; Hutton scribes the absorption spectra of all types of irradia- 370 J. Gemm., 1989,21,6 ted smoky and greenish-yellow quartz crystals to be the independent nature of this third type of citrine due to a superposition of an absorption maximum in coloration is recognized, were published by the ultraviolet, the low energy tail of which extends Samoilovich et al. (1976) and Lehmann (1977, to the visible area (so-called greenish-yellow absorp­ 1978a). Further information about this type of tion) with several distinct absorption maxima at citrine coloration is found in the publications of 15,000 cm-1 (designated A0, 20,650 cm-1 (desig­ Nassau and Prescott (1977a), Steshchin (1979a,b), -1 nated A2), 23,400 cm (designated A3, smoky Maschmeyer et al. (1980), Lehmann (1981) and colour centre) and 32,000 cm-1 (designated B) Maschmeyer and Lehmann (1983). (Nassau and Prescott, 1975,1977a). The absorption spectrum of this third type of In the first group of publications, besides an citrine is similar to the spectrum of heat-treated absorption maximum in the ultraviolet causing an amethyst, i.e. the spectrum consists of a strong increasing absorption from red to violet in the absorption in the ultraviolet area, the low energy tail visible region, two different types of colour centres of which extends to the visible region. Instead of the are assumed to be additionally present in the visible coloration of heat-treated amethyst, natural un­ part of the absorption spectra of quartz crystals with treated citrine of this third type is slightly smoky brown, yellowish-grey, and greenish-yellow pleochroic. The difference between artificially colours. In these varieties of irradiated quartz irradiated greenish-yellow quartz, i.e. the second crystals, the ordinary smoky centre is thought to be type of citrine, and this third type of citrine responsible for the absorption band at about 22,200 coloration is the absence of a distinct absorption cm-1 (450 nm), and a similar, but not identical band at about 25,000 cm-1 (400 nm) as well as an colour centre is thought to cause the absorption improved thermal stability of the colour centres up band at about 25,000 cm-1 (400 nm). The various to about 500°C. A model for two paramagnetic colour shades of irradiation-treated samples with or centres observed in two crystals of this third type of without subsequent annealing are explained by citrine from Madagascar was worked out by combinations of the ultraviolet absorption maxi­ Maschmeyer et al. (1980) and Lehmann (1981), and mum with the two absorption bands in the blue and new investigations by Maschmeyer and Lehmann violet, all three of them having different intensity (1983) using natural citrines from Madagascar ratios as well as different bleaching characteristics. revealed the presence of at least seven different hole In the second group of publications all different centres. Most of them are related to substitutional smoky to greenish-yellow colour shades of irradia­ Al on Si sites; however, the exact nature of addition­ ted quartz crystals are explained by combinations of al defect structures which cause their difference to two absorption bands only, i.e. by a superposition of smoky quartz centres are still unknown. the greenish-yellow absorption in the ultraviolet The unique green quartz described by Nassau and the ordinary smoky absorption band. The and Prescott (1977b) is possibly a citrine of this presence of a different third absorption band, the third type having an additional weak absorption maximum of which is shifted from 22,200 cm-1 to band at about 16,100 cm-1 (620 nm), the origin of the short wavelength region is not assumed in those which is unknown at present. papers (cf. also the results of Sawyer, 1974,1976). II. 4 SYNTHETIC FE-CONTAINING YELLOW, GREEN, 3+ 4+ In general, Al on Si sites with charge com­ ORANGE-BROWN AND BROWN QUARTZ pensating alkali ions is thought to be responsible for The first samples of synthetic brown and green the formation of smoky colour centres in quartz, 3+ 4+ quartz were described by Tsinober et al. (1959), and Al on Si sites with charge compensating Tsinober and Chentsova (1959) and Ballmann hydrogen and lithium ions is assumed to cause (1961). The crystals were grown on basal seeds in greenish-yellow colours. However, not all details of aqueous K2C03-containing solutions by hydro- irradiation-induced smoky and greenish-yellow col­ thermal techniques. Brown crystals containing our centres are understood at present. mainly Fe3+ were obtained from lower concentra­ 3+ tions of K2C03 and green crystals containing Fe II. 3 NATURAL YELLOW TO BROWN QUARTZ AND 2+ HEAT-TREATED MORION and Fe were grown from solutions with very high Natural yellow and light brown quartz, which is K2C03 concentrations. Heat treatment at 400 - not produced from amethyst by heat treatment, is 500°C turned brown crystals green by reducing part 3+ 2+ long known in the gem trade. Part of the material ofFe toFe . used for cutting purposes is of natural colour, i.e. The growth of synthetic yellow quartz, so-called these stones are neither heat-treated nor artificially- synthetic citrine, is described comprehensively by irradiated. In some instances, natural smoky quartz Chadschi and Reschetowa (1975) and Khadzhi and or morion is able to be converted by heat treatment Reshetova (1977). The crystals were grown on at about 300°C to yellow or light brown citrine (cf. quartz seeding plates orientated parallel to the basal Wild, 1968; Bank, 1976). The first papers, in which pinacoid (0001) or with plates inclined at an angle 1-J. Gemm.,Gemm., 1989,21,61989,21,6 371371

TableTable 1.1. AbsorptioAbsorptionn bandsbands assignedassigned toto trivalentrivalentt ironiron inin interstitialinterstitial sitessites ofof distorteddistorted tetrahedratetrahedrall symmetrysymmetry inin thethe quartzquartz latticelattice (in(in cmcm -[)-1) Lehmann,Lehmann, 1971a1971a KhaliovKhaliovera/. et ai.,, 19791979 TransitionTransition 18,70018,700 18,00018,000 %T%

20,20020,200 20,30020,300 ~'1'2->

4 4 22,50022,500 21,80021,800 ~4Ab-+ Ab 4EE 22,70022,700

24,80024,800 24,80024,800 ~-*T '1'22

27,30027,300 26,00026,000 ~4E-+4E

29,10029,100 28,70028,700 ~'1'[4»-p

withiwithinn thethe rangerange ofof uupp ttoo 20°20° ttoo ththee basalbasal planeplane inin clescles oror ionsions areare presenpresentt inin variouvariouss amounts,amounts, andand thethe aqueousaqueous solutionssolutions ofof K2C033.• Furthermore,Furthermore, sub­sub- colourcolour isis duedue toto a superpositionsuperposition ofof threthreee basicbasic typestypes stancesstances forfor thethe oxidationoxidation ofof ironiron suchsuch asas nitritenitritess andand ofof absorptionabsorption spectra.spectra. nitratesnitrates ofof alkalialkali metalsmetals oror potassiumpotassium permanganatepermanganate TheThe spectrumspectrum ofof iron-containingiron-containing colloidalcolloidal par­par­ (e.g.(e.g. LiNOz,LiN02, NaN0NaNOz,2, KN0KNOz,2, LiN033, NaN03, ticleticless consistsconsists ofof a strongstrong absorptionabsorption inin thethe ultra­ultra­ KN033,, KMn04)KMn04) areare addedadded ttoo thethe solution.solution. TheThe violetviolet,, thethe lowlow energyenergy taitaill ofof whicwhichh extendsextends toto thethe + presencepresence ooff Li + inin ththee workinworkingg solutionsolution ofof K 2C03 isis visiblvisiblee area.area. A continuouscontinuous absorptionabsorption resultsresults in­in­ responsibleresponsible forfor purificationpurification fromfrom undesireundesiredd alu­alu­ creasingcreasing fromfrom reredd toto violet.violet. IInn ththee absorptionabsorption 33+ miniumminium impuritiesimpurities duedue toto thethe formationformation ofof hardlyhardly spectrumspectrum ofof Fe + (14)(I4) numerousnumerous weaweakk absorptionabsorption solublesoluble impuritiesimpurities suchsuch asas eucryptite,eucryptite, LiAISi0LiAlSi04. bandsbands areare foundfound inin ththee visiblvisiblee andand ultravioleultraviolett regionregion 2+ WithouWithoutt ththee presencepresence ofof lithiumlithium ions,ions, capillarycapillary (Table(Table 1).1). TheThe spectrumspectrum ofof Fe + (16)(I6) isis dominateddominated channelschannels paralleparallell ttoo thethe opticaloptical axisaxis ofof thethe quartzquartz bbyy twtwoo strongstrong broabroadd absorptionabsorption bandsbands withwith maximamaxima crystalscrystals areare formedformed bbyy AAll impurities,impurities, disturbingdisturbing thethe atat aboutabout 13,50013,500 andand 10,50010,500 cm -[-1 (741(741 andand 950950 nm).nm). homogenithomogenityy andand colourcolour qualityquality ofof syntheticsynthetic citrine.citrine. InIn yelloyelloww toto orange-brownorange-brown quartquartzz growgrownn inin A thirthirdd methodmethod forfor thethe productionproduction ofof iron­iron- K2C03 solutionssolutions withwith thethe presencespresences ofof oxidizingoxidizing bearinbearingg yellowyellow toto orange-brownorange-brown quartzquartz isis recentlyrecently phasesphases,, iron-containingiron-containing particlesparticles areare dominant.dominant. InIn describeddescribed bbyy HosakaHosaka andand TakiTaki (1983).(1983). TheThe hydro­hydro- brownbrown quartzquartz fromfrom K2C03 solutionssolutions withouwithoutt thethe thermathermall growthgrowth wawass performeperformedd usinusingg NaClNa~l-- andand presencpresencee ooff oxidizers,oxidizers, iron-containingiron-containing particlesparticles andand 3 + KCl-containingKCl-containing solutionssolutions witwithh X-cutX-cut (1120)(1120) andand Fe + (14)(I4) areare observed.observed. InIn greengreen quartz,quartz, additionaladditional 2+ Y-baY-barr seeds.seeds. amountsamounts ofof Fe + (16)(I6) areare found.found. AlAlll colourscolours ooff VariousVarious publicationspublications dealdeal withwith colourcolour anandd colourcolour iron-containingiron-containing syntheticsynthetic quartzquartz cancan bebe explainedexplained causescauses inin syntheticsynthetic Fe-containingFe-containing yellowyellow,, brownbrown bbyy a combinationcombination ofof allall threthreee colour-causingcolour-causing par­par­ andand greengreen quartzquartz (Lehmann(Lehmann andand Moore,Moore, 1966;1966; ticlesticles oror ionsions inin variousvarious concentrations.concentrations. UpoUponn heatheat Lehmann,Lehmann, 1967,1967,1971a,b 1971a,b;; SamoilovichSamoilovich etal.,er a/., 1969a;1969a; treatment,treatment, brownbrown samplessamples ofof iron-containingiron-containing synth­synth­ GordienkoGordienko et ai.,al., 1969;1969; LehmannLehmann andand Bambauer,Bambauer, eticetic quartzquartz areare convertedconverted toto greengreen prasioliteprasiolite.. ThisThis 1973;1973; SamoilovichSamoilovich et aI.,al., 1976;1976; ZakharovZakharov et ai.,al., colourcolour changechange isis explainedexplained bbyy a reductionreduction ofFeof FeH3+ toto 1978;1978; KhaliovKhaliov et ai.,al, 1979;1979; BalakirevBalakirev et aI.,al, 19791979;; Fe2+Fe2+ accompaniedaccompanied byby a migrationmigration fromfrom tetrahedraltetrahedral H3+ 2+ BalitskyBalitsky andand Balitskaya,Balitskaya, 1985,1985, 1986).1986). SomeSome ofof thethe toto octahedraloctahedral interstitialinterstitial sites,sites, i.e.i.e. Fe (14)(I4) —~> Fe2+Fe resultresultss cancan bbee summarizedsummarized asas followsfollows:: inin syntheticsynthetic (I(1 6) (Tsinoberet(Tsinoberef aI.,a/., 1959;1959; SamoilovichSamoilovich et ai.,al., 1969a;1969a; yellow,yellow, orange-brown,orange-brown, browbrownn andand greengreen quartzquartz LehmannLehmann andand Bambauer,Bambauer, 1973).1973). threthreee differentdifferent colourcolour causescauses werweree foundfound ttoo exist.exist. TheseThese areare iron-containingiron-containing colloidalcolloidal particles,particles, mostmost 11.5II. 5 YELLOWYELLOW,, GREENISH-BROWNGREENISH-BROWN ANDAND YELLOW­YELLOW- probablyprobably FeFe203,203, ferricferric ironiron onon interstitialinterstitial sitessites ooff BROWN,BROWN, IRRADIATION-TREATEDIRRADIATION-TREATED SYNTHETICSYNTHETIC distorteddistorted tetrahedraltetrahedral co-ordination,co-ordination, designateddesignated QUARTZQUARTZ (ORIGINALLY(ORIGINALLY COLOURLESS)COLOURLESS) 3 + Fe + (1(I4),), andand ferrousferrous ironiron onon interstitialinterstitial sitessites ooff Irradiation-inducedIrradiation-induced colourcolour changeschanges ofof syntheticsynthetic distorteddistorted octahedraloctahedral co-ordination,co-ordination, designateddesignated Fe2+Fe2+ quartzquartz areare slightlyslightly differentdifferent fromfrom colourcolour changeschanges ofof (I(16)'6). AccordinAccordingg ttoo ththee detailsdetails ooff crystalcrystal growthgrowth ooff anan irradiation-treatedirradiation-treated naturalnatural samples.samples. InIn syntheticsynthetic individualindividual sample,sample, thethe threthreee colour-causingcolour-causing parti-parti­ quartz,quartz, smokysmoky andand greenish-yellowgreenish-yellow colourscolours areare 372 J. Gemm., 1989,21,6 obtainable after irradiation (Gordienko et al., 1969; Ill Investigations of commercially available, and Sawyer, 1974, 1976; Samoilovich et al, 1976; some non-commercially, natural and synthetic Nassau and Prescott, 1977a). Subsequent heat citrines including yellow, yellowish-green, green, treatment turns smoky quartz blue, blue-green, orange-brown and brown quartz varieties green, greenish-yellow or colourless, whereas green­ III. 1 MATERIALS AND METHODS ish-yellow quartz is only bleached by annealing Only few references are found in literature which processes (Nassau and Prescott, 1977a). In some contain specific indications on techniques applic­ papers, a correlation between trace element con­ able for the distinction of natural and synthetic tents and irradiation-induced colour centres is citrine (cf. O'Donoghue, 1983). In the present discussed, e.g. for Al- and Ge-containing synthetic research project, the two main methods which were quartz with smoky coloration after gamma irradia­ suggested for the distinction of natural and syn­ tion (Chentsova and Butuzov, 1962; Haven et al., thetic amethyst, i.e. infrared spectroscopy and 1966; Tsinober et al., 1967; Gordienko et al., 1969) microscopic determination of twinning, growth as well as for Ga-containing synthetic quartz with structures and inclusions, were also tested for the yellow-brown coloration after irradiation treatment determination of citrine. According to Zecchini and (Balitskii et al., 1970). The influence of charge Mérigoux (1980), infrared spectroscopy in the compensating hydrogen and alkali ions (sodium 4000-3000 cm"l range is useful for the distinction of and lithium) is also questionable (cf. Sawyer, 1974, natural and synthetic citrine. However, experi­ 1976). However, not all details of irradiation- ments performed by Th. Lind at Heidelberg Uni­ induced colour changes of synthetic quartz are versity in 1982 and 1983 (unpublished) using understood at present. heat-treated amethysts and Fe-containing synthetic For jewellery purposes, synthetic quartz crystals citrines were not successful and failed to establish with irradiation-induced yellow, greenish-yellow or infrared spectroscopy as a routine method for the yellow-brown coloration are not suitable due to the determination of cut citrines of unknown origin. low thermal stability of this type of citrine colour According to microscopic investigations, the rec­ centres (Nassau and Prescott, 1977a), which are ognition of the presence of polysynthetic twinning already bleaching in daylight (Balitsky, 1981). on the Brazil law is useful for the determination of natural citrine which is produced from natural amethyst by heat treatment (Schmetzer, 1985, 1986). This result was worked out using a horizon­ II. 6 SYNTHETIC CO-CONTAINING YELLOW, BROWN tal microscope with immersion liquids and an AND BLUE QUARTZ especially developed sample holder. By the applica­ Co-bearing synthetic quartz is grown from tion of a simplified technique for the recognition of Na2COr and K2C03-containing solutions on basal polysynthetic twinning in natural amethyst without seed plates. The colour of the samples obtained are microscopic investigations, an identical behaviour blue from Na2C03- and yellow to brown from of natural amethyst and citrine produced by heat K2C03-containing environments, respectively. The treatment of natural amethyst is described (Crown- absorption spectra of blue samples are assigned to ingshield etal., 1986). This statement, however, was bivalent cobalt in interstitial positions of distorted found to be partly incorrect and thus will be 2+ tetrahedral symmetry, designated Co (I4), where­ discussed below in detail. as the spectra of brown cystals are explained by the In summary, it was assumed at the beginning of presence of trivalent cobalt in interstitial positions 3+ the present investigation, that the determination of of distorted octahedral symmetry, designated Co twinning and other structural properties can be a (I6). Brown samples turn blue after heat treatment useful method for the characterization of citrines of at approximately 450°C. This colour change is due unknown origin whereas the application of infrared to a reduction of cobalt from trivalent to bivalent spectroscopy for the study of citrines, especially for state accompanied by a displacement from distorted faceted samples, was neglected in this project. octahedral to tetrahedral interstitial positions, i.e. 3+ 2+ However, it is evident from literature (cf. sections Co (I6) -* Co (I4) (Wood and Ballman, 1966; II. 1-II. 6), that different natural and synthetic Samoilovich et al., 1969a; Gordienko et ah, 1969; varieties of citrine reveal various colour causes. Lehmann, 1969, 1971a; Lehmann and Bambauer, 3+ Thus, the investigation of absorption spectra in the 1973). In addition to the presence of Co (I6)3 visible and ultraviolet region was assumed to be an synthetic samples may also contain distinct 3+ adequate method to characterize the samples. In amounts of Fe , most presumably as colloidal addition, it was suspected that possibly some particles (Gordienko et al., 1969; Lehmann, 1969; spectroscopic properties of natural and synthetic Balakirev et al., 1979). At present, no natural citrines are not common for all types of samples. counterparts of synthetic Co-bearing blue, yellow or These considerations led to systematic investiga­ brown quartzes are known. tions by a combination of microscopy and absorp- J. Gemm., 1989,21,6 373

tion spectroscopy in the visible and ultraviolet. of this particular type of citrine. The absorption The samples investigated were selected in order maximum in the ultraviolet extending to the visible to be typical and representative for the material is assigned to iron-containing colloidal particles in used in the gem industry of Idar-Oberstein. For literature, which are formed during the annealing most natural samples, the exact localities were process. The weak absorption band at 21,000 cm-1 known. In contrast, no synthetic samples were was not mentioned previously. found in the trade, for which an appropriate The absorption spectra of heat-treated natural characterization of growth conditions was available amethysts which turned green during the anneahng and, therefore, the assignment of the samples process, the so-called prasiolite of the trade (Figure investigated to certain categories of synthetic cit­ 2), show an additional weak absorption band at rine as well as to specific growth conditions had to about 13,500 cm-1 (741 nm), which was assigned to be worked out experimentally. bivalent iron on interstitial sites of distorted

Fig. 1. Colour sequence of natural citrines; five samples represent heat-treated natural amethysts from Brazil, the right stone represents natural untreated citrine from Goyaz, Brazil. Diameter of the sample approx. 10 mm. Photo by O. Medenbach, Bochum, FRG.

2+ III. 2 RESULTS octahedral symmetry, Fe (I6). The colour of III.2.1 Heat-treated natural amethyst {citrine and heat-treated amethyst is dependent only of the prasioUte) intensity ratios of the green and yellow to brown Yellow to orange-brown citrine and green absorption, i.e. the colour after anneahng is due to prasiolite which was commercially produced by the relative amounts of iron-containing precipitates 2+ anneahng of natural amethyst was available from and Fe (I6) produced by heat treatment. How­ different localities in Brazil, from Uruguay and ever, the detailed mechanisms of the development Namibia. The designations Bahia, Palmeira and of both types of iron in various ratios are not Madeira citrine are sometimes used in the trade in completely understood at present (cf. Neumann order to characterize the colour intensity of samples and Schmetzer, 1984a,b). in the yellow to orange-brown sequence (Figure 1), Polysynthetic twinning on the Brazil law is greened amethyst is often called prasiolite. thought to be one of the most important properties Absorption spectra of this type of natural citrine of natural amethyst, the presence of which can be (heat-treated amethyst) reveal a continuously in­ used for recognition of an unknown sample to be of creasing absorption from red to violet in all samples natural origin. Unfortunately, the possibility for with different colour shades and intensities (Figure direct observation of polysynthetic twinning on the 2). The increasing absorption is caused by a strong Brazil law in natural amethyst and heat-treated band with maximum in the ultraviolet, the low natural amethyst (citrine and prasiolite) is limited to energy tail of which extends to the whole visible a small number of specimens only (cf. Schmetzer, area. In addition, a weak absorption band at about 1987). However, the presence of polysynthetic 21,000 cm-1 (476 nm) was measured in all samples twinning is clearly indicated by the observation of 374 J. Gemm., 1989,21,6

WAVELENGTH (rim) 350 400 500 600 700

~ 6 <= ~ s 6 :ii "{ 6

6

66

6

7

8

9 05 I 10

30 25 20 15 WAVENUMBER (lOOO crrr l )

Fig. 2. Absorption spectra of natural citrines and natural prasiolites (heat-treated natural amethysts); citrines: 1 Brazil, 2 Brazil, 3 Brazil, 4 Uruguay,S Brazil, 6 Maramba, Brazil, 7 Bahia, Brazil; prasiolites: 8 jakobina, Brazil, 9 Montezuma, Brazil, 10 Zambia. J. Gemm., 1989,21,6 375

aba b ba b · r c ~-~..... :/~~ li-X z a b

r

aba abab r

Fig. 3. Idealized drawings of natural citrine (heat-treated natural amethyst) in a view parallel to the c-axis showing the model of polysynthetic twinning on the Brazil law after McLaren and Pitkethly (1982) and the orientation of striations in growth sectors confined to the major and minor rhombohedron rand z. Left: quartz crystals with right-handed (R) or left-handed (L) quartz in the centre. Brewster fringes (extinction bands) in growth sectors confined to the major rhombohedral faces r {lOll} separate lamellae of right-handed and left-handed quartz, a single twin boundary enters each growth sector confined to the minor rhombohedron z {Olll}. Centre: the directions of the double-headed arrows (which are represented by the symbols a, b and c) correspond to traces of the predominant twin boundaries; in subsequent Brewster fringes, alternating directions of predominant twin boundaries are observed. Right: directions of orientated striations in growth sectors confined to the major and minor rhombohedron rand z in crystals with right-handed and left-handed quartz in the centre.

extinction bands (so-called Brewster fringes) in According to the experience of the present author, polarized light under crossed polarizers provided both versions of the method yield similar or identi­ that the optic axis of the amethyst is arranged cal results for large cut stones. However, for smaller parallel to the line of sight. The investigation is stones in the range of about 0.5 to 2.0 carats in possible in the horizontal microscope in combina­ weight, the application of the microscope may be tion with an immersion cell and immersion liquids. necessary. In addition, samples from distinct locali­ For convenient handling, the use of an improved ties, e.g. samples from Para, Brazil, reveal an sample holder with horizontal and vertical rotation extremely complicated twinning structure. For the axes is suggested (Schmetzer, 1985, 1986). recognition of such samples as well as for a distinc­ A somewhat simplified method was described by tion from that particular type of twinning, which is Crowningshield et al, (1986), using a standard found in synthetic amethyst (cf. Lind and Schmet­ gemmological polariscope with an immersion cell. zer, 1985, 1987),the authorfeels that the application 376 J. Gemm.,1989,21,6

Fig. 4 Fig. 5

Fig. 6 Fig. 7

Fig. 8 Fig. 9

Fig. 10 Fig. 11 J. Gemm.,1989,21,6 377 of the gem microscope yields more reliable results. polysynthetic lamellae of right-handed and left- Furthermore, diagnostic structures in heat-treated handed quartz. However, growth sectors confined amethyst may be extremely complicated thus to the major and minor rhombohedron r and z are favouring the investigation by use of the micro­ still observable in the gem microscope. They are scope. frequently recognizable due to different colour In heat-treated natural amethyst two basic types intensities with a more intense brown or yellow hue of diagnostic structures and one group of samples in growth sectors confined to the major rhom­ with an intermediate type of characteristics are bohedron r and a less intense brownish or yellow observable. In the first group of samples, the hue in sectors confined to the minor rhombohedron twinning structures of untreated amethyst are com­ z (cf. colour zoning in heat-treated bicolour ameth­ pletely preserved during the annealing process. The yst-citrine quartz; Nassau, 1981). In addition, growth sectors of the stones, which_are confined to boundaries^between different growth sectors are the major rhombohedron r {1011}, consist of distinctly outlined and orientated striations of dark polysynthetically twinned lamellae of alternating brown colour are found in different directions right-handed and left-handed quartz. The growth confined to different growth sectors r and 0, respec­ sectors confined to the minor rhombohedron tively (Figures 11, 12). In growtl\sectors confined z {0111} do not show this type of twinning on to the minor rhombohedron z {0111}, these brown the Brazil law; only one single twin boundary striations are orientated perpendicular to the three entering each z growth sector is observed (Figure 3, prism faces {0110}. In growth sectors confined to for a more detailed description the reader is referred the major rhombohedron r {1011}, two different to the papers of Schlössin and Lang, 1965; orientations of the brown striations exist, which are McLaren and Pitkethly, 1982; Schmetzer, 1985, dependent on the nature of the centre of the 1986, 1987 as well as Crowningshield et al., 1986). untreated crystal, which may consist of right- Typical microphotographs of interference figures of handed or left-handed quartz. Schematic line draw­ this group of samples are pictured in Figures 4-6. ings of the two possibilities mentioned are given in The second important group of heat-treated Figure 3. At present, no description or interpreta­ amethyst does not show interference figures which tion of this particular type of orientated striations are related to polysynthetic twinning on the Brazil are known to the present author from literature. law. In other words, investigations of this group of Most probably, the disappearance of polysynthetic samples under crossed polarizers yield interference twinning on the Brazil law as well as the develop­ figures which are comparable to the interference ment of orientated brown striations is due to the patterns of quartz crystals, which do not consist of annealing of natural samples. However, additional

Fig. 4. Natural citrine (heat-treated natural amethyst) from the major rhombohedron r and not in growth sectors Brazil; interference figure showing polysynthetic twin­ confined to the minor rhombohedron z, a single twin ning in three growth sectors confined to* the major boundary enters one growth sector confined to the rhombohedron r; a drill-hole is running through the minor rhombohedron z\ striations orientated according centre of the bead. Crossed polarizers. 20x. to the growth sector they are confined to. Crossed Fig. 5. Natural citrine (heat-treated natural amethyst) from polarizers. 26x. Maramba, Brazil; interference figure showing poly­ synthetic twinning in two growth sectors confined to Fig. 9. Natural citrine (heat-treated natural amethyst) from the major rhombohedron r and not in growth sectors Brazil; highly distorted interference figure showing confined to the minor rhombohedron z. Crossed pola­ polysynthetic twinning in three growth sectors con­ rizers. 16x. fined to the major rhombohedron r and not in growth Fig. 6. Natural citrine (heat-treated natural amethyst) from sectors confined to the minor rhombohedron z; stria­ Brazil; interference figure showing a single boundary tions orientated according to the growth sector they are entering one growth sector confined to the minor confined to. Crossed polarizers. 20x. rhombohedron z. Crossed polarizers. 30x. Fig. 10. Natural citrine (heat-treated natural amethyst) from Fig. 7. Natural citrine (heat-treated natural amethyst) from Uruguay; highly distorted interference figure showing Brazil; distorted interference figure showing poly­ polysynthetic twinning in three growth sectors con­ synthetic twinning in three growth sectors confined to fined to the major rhombohedron r and not in growth the major rhombohedron r and not in growth sectors sectors confined to the minor rhombohedron z\ stria­ confined to the minor rhombohedron z, a single twin tions orientated according to the growth sector they are boundary enters one growth sector confined to the confined to. Crossed polarizers. 20x. minor rhombohedron z; striations orientated according Fig. 11. Natural citrine (heat-treated natural amethyst) from to the growth sector they are confined to. Crossed Brazil; interference figure showing no polysynthetic polarizers. 14x. twinning on growth sectors confined to the major and Fig. 8. Natural citrine (heat-treated natural amethyst) from minor rhombohedra r and z; striations orientated Brazil; distorted interference figure showing poly­ according to the growth sector they are confined to. synthetic twinning in three growth sectors confined to Crossed polarizers. 40x. 378 J. Gemm., 1989,21,6 investigations are necessary in order to clarify (Figure 1). According to the informations given by details of the process. Using a simplified technique the suppliers, these samples were not artificially without microscopic examination as described by heat-treated. However, samples of this type of Crowningshield et al. (1986), this second group of citrine with more intense smoky coloration are natural citrine originating from heat-treated ameth­ known for a long time in the trade. In samples of yst yields the interference figure of untwinned this particular type (natural smoky quartz), smoky quartz under the polariscope. Consequently, this coloration is commercially removed by heat- type of heat-treated amethyst does not behave in the treatment. polariscope in the same manner as natural amethyst. The samples available for the present investiga­ The third intermediate group of samples of tion were not altered by heat treatment up to about heat-treated natural amethyst shows more or less 375°C. At 400°C the yellow coloration became distorted interference figures as well as more or less lighter and was completely bleached at tempera­ intense orientated brown striations (Figures 7-10). tures between 450 and 550°C. Exposition of heat- These observations are explainable by a decrease of treated (colourless) and non-heat-treated (yellow) polysynthetic twinning on the Brazil law parallel to samples to gamma rays (dose rate about 30 Mrads) a development of orientated striations, the direc­ or neutrons (integrated fluence rate about 3 x 1015 tions of which are dependent on the respective n/cm2) turned all samples an intense smoky colora­ growth sector which they are confined to. tion, which was bleached at temperatures between Lamellar growth structures, parallel to the major about 225 and 275°C. The resulting yellow or and minor rhombohedron, which are frequently greenish-yellow coloration was stable up to 450- connected with colour zoning, are most common in 550°C in samples, which were not bleached artifi­ natural amethyst. These zonal growth structures cially before and up to 325°C in artificially bleached are still observable in all types of heat-treated samples. These results indicate, that an almost natural amethyst. In most samples, sharp lamellar identical yellow or greenish-yellow coloration which structures parallel to several rhombohedral faces are is caused by colour centres with lower stability was found, incidentally growth structures parallel to the induced in colourless samples or superimposed on hexagonal prism faces were also present. In a high the natural yellow coloration in unbleached samples percentage of samples, families of straight parallel by exposure to gamma rays and neutrons. This type growth planes parallel to the major and minor of artificially-induced coloration will be described rhombohedron were observed, which form two in the following chapter, more experimental details characteristic angles of 94° (Figure 13, formed by have been published elsewhere (Schmetzer, 1988). the two faces r and r' or z and z'\ 134° (Figure 14; The absorption spectra of all samples of non- formed by two adjacent rhombohedral faces r and z) artificially-irradiated citrine from different locali­ as well as 76° (Figure 15; formed by two opposite ties (Figure 17) consist of an absorption band in the rhombohedral faces r and z). Angular growth ultraviolet, the low energy tail of which extends to structures between prism and rhombohedral faces, the visible region causing a continuously increasing forming an angle of 142° were found to be extremely absorption from red to violet. In some samples an rare. additional weak absorption band at about 15,500 -1 According to information from the trade, only cm (645 nm) was measured (Figure 17). internally flawless material of natural amethyst Microscopic examinations of this type of natural without healing feathers consisting of liquid and citrine reveal the presence of diagnostic properties two-phase inclusions are selected for heat treatment only in part of the samples. Some rough or cut due to the formation of fissures and cracks in stones were internally flawless and did not show impure samples. Thus, the absence of healing growth structures or twinning on the microscope feathers in commercially heat-treated amethyst is scale, i.e. no interference figures of poly synthetical­ explained, which was confirmed by microscopic ly twinned quartz were observed (Figure 18). investigations of numerous samples. Only inciden­ Incidentally, in stones from Brazil and Madagascar tally, the presence of black or reddish-brown solid thin plates or bodies were found to be inserted in the state inclusions of iron oxides or hydroxides was crystals (Figure 19). Most probably, the samples are observed (Figure 16). macroscopically twinned on the Brazil law, as described comprehensively by various authors, e.g. III.2.2 NON-ARTIFICIALLY-IRRADIATED NATURAL Frondel(1962). CITRINE In samples from Brazil and Spain, growth struc­ Natural citrines in the colour sequence light tures were sometimes observed in the form of single yellow, yellow, brownish-yellow and greyish-yellow growth planes which are orientated parallel to the were available from localities in Bahia and Goyaz, prism faces m {1120} as well as parallel to _the Brazil, from Salamanca, Spain and Madagascar rhombohedral faces r {1011} and z {0111} J. Gemm., 1989,21,6 379

WAVELENGTH (run)

350 400 500 600 700

~ <: gs~ :fl '<:(

2

3

I05 4

30 25 20 15 WAVENUMBER ( 1000 crrrl )

Fig. 17. Absorption spectra of natural citrines; 1 Salamanca, Spain, 2 Goyaz, Brazil, 3 Madagascar, 4 Bahia, Brazil.

of the crystals (Figures 20, 21). Occasionally, in lighter yellowish-grey colour. Subsequent heat citrines from Goyaz, Brazil, double refracting treatment at 200°C bleached part of the irradiation mineral inclusions were found to be confined to the induced smoky colour centres. After annealing of growth boundaries parallel to prism and rhom­ the samples at 225, 250 or 275°C, the smoky colour bohedral faces (Figure 21). These mineral inclu­ centres were completely bleached and the colour of sions were not yet determined exactly. In citrine the samples was identical to the as-received form. crystals from all localities investigated, healing Subsequent heat treatment to 325 or 350°C again feathers consisting of liquid and two-phase inclu­ bleached the greenish-yellow colour. sions were also present incidentally (Figure 22). Absorption spectra of one typical sample are 111.2.3 ARTIFICIALLY-IRRADIATED NATURAL CIT­ presented in Figure 23. In the as-received greenish­ RINE (ORIGINALLY COLOURLESS) yellow coloration, the absorption spectrum ofthe Some samples of artificially-irradiated greenish­ quartz crystal is composed of an absorption band in yellow citrine from unknown localities were made the ultraviolet, the low energy tail of which extends available for investigation. The colour was com­ to the visible region. This increasing absorption pletely bleached at 325 or 350°C. After irradiation from red to violet is superimposed by two absorp­ with gamma rays (dose rate about 30 Mrads), the tion bands with maxima at about 15,500and 26,000 stones turned an intense greyish-black (smoky) or a cm" (645 and 385 om). After irradiation, the 380 J. Gemm., 1989,21,6

Fig. 12. Natural citrine (heat-treated natural amethyst) from Fig. 13. Natural citrine (heat-treated natural amethyst) from Brazil; interference figure showing no poly synthetic Brazil; families of straight parallel growth planes twinning on growth sectors confined to the major and parallel to the major rhombohedron r and r' {1011} minor rhombohedra r and z\ striations orientated forming an angle of 94°. 30x. according to the growth sector they are confined to. Crossed polarizers. 30x.

Fig. 14. Natural citrine (heat-treated natural amethyst) from Fig. 15. Natural citrine (heat-treated natural amethyst) from Brazil; families of straight parallel growth_ planes Brazil; families of straight parallel growth_ planes parallel to the major rhombohedron r _(1011) and parallel to the major rhombohedron r_(1011) and parallel to the minor rhombohedron z (Oil 1) forming parallel to the minor rhombohedron z (0111) forming an angle of 134°, different colour intensities are an angle of 76°, different colour intensities are observ­ observable in the growth sector confined to r (dark able in the growth sector confined to r (dark orange- orange-brown) and the growth sector confined to z brown) and the growth sector confined to z (light (light orange-brown). 30x. orange-brown). 26x. additional absorption bands of smoky colour cen­ By microscopic investigations, the presence of tres with absorption maxima at about 22,200 cm-1 small healing feathers in part of the citrines of this (450 nm) are observable. Heat treatment between type was observed. 200 and 325°C in intervals of 25°C each (annealing time 0.5 h at each step) caused first a bleaching of III. 2.4 HEAT-TREATED SYNTHETIC AMETHYST these additional smoky colour centres and subse­ Synthetic amethysts commercially grown in quently a bleaching of the group of three absorption Japan and USSR were annealed at various tempera­ bands at 15,500 and 26,000 cm-1 and in the tures. The amethyst colour centres bleached at ultraviolet (Figure 23). about 460°C and the samples turned colourless. No These results indicate that the greenish-yellow yellow or brown coloration was developed at anneal­ quartz crystals received from the trade are artificial­ ing temperatures and times up to 600°C and 24 h, ly irradiated samples, the smoky coloration of respectively. However, the violet amethyst colora­ which were bleached by heat treatment at about tion was completely restored after subsequent gam­ 250°C. After complete bleaching, the smoky and ma irradiation. This unexpected result indicates a greenish-yellow colour centres are restored by re- stabilization of both precursor centres of the ame­ irradiation. thyst colour centre, i.e. trivalent iron on substitu- J. Gemm., 1989,21,6 381

Fig. 16. Natural citrine (heat-treated natural amethyst) from Fig. 18. Natural citrine from Goyaz, Brazil; interference figure Namibia; black mineral inclusions (Fe-oxides or hyd­ of an optically untwinned crystal. 20x. roxides). 65x.

Fig. 19. Natural citrine from Brazil; isolated Brazil twin within Fig. 20. Natural citrine from Brazil; growth planes parallel to an optically untwinned crystal showing interference the major rhombohedron r_(1011) and parallel to the colours and interference striations at the twin boun­ minor rhombohedron z (0111) forming an angle of 76°. daries. Crossed polarizers. 16x. 34x.

Fig. 21. Natural citrine from Brazil; growth planes parallel to Fig. 22. Natural citrine from Goyaz, Brazil; healing feather the hexagonal prism (1010), double refracting mineral consisting of liquid and two phase inclusions. 45x. inclusions are confined to one growth plane. 45x. 382 J. Gemm., 1989,21,6

WAVELENGTH (nm)

350 400 500 600 700

~ <: g;~ :il :- 2

10:-- J,

30 25 20 15 WAVENUMBER ( 1000 crrrl } Fig. 23. Absorption spectra of artificially-irradiated natural crtrme (originally colourless); I sample in the as-received form (greenish-yellow); 2 sample after heat treatment at 325'C (colourless) and subsequent gamma irradiation (yellowish-grey); 3a-e irradiation-treated sample after subsequent heat treatment at 200'C (3a, greyish-yellow), 225'C (3b, greenish-yellow), 250'C (3c, greenish-yellow), 275'C (3d, light greenish-yellow), 300'C (3e, very light yellowish), 325'C (not pictured, colourless). tional silicon sites and on interstitial sites of dis­ information which was given by the trade. Accord­ torted tetrahedral symmetry, which is different ing to their diagnostic features, the samples were from the stabilization of the amethyst precursor subdivided into several groups with identical or centres in most natural samples. similar properties. In some cases, it was evident that a distinct type of synthetic Fe-containing citrine 111.2.5 SYNTHETIC FE-CONTAINING YELLOW, was grown by different producers using closely GREEN AND BROWN QUARTZ (INCLUDING FE- AND related or almost identical growth conditions. In CO-BEARING SAMPLES) other cases, it may be possible that samples from Most samples of synthetic Fe-bearing quartz different producers or different producing coun­ with yellow, green and brown coloration, which tries were mixed with or without intention. There­ were made available for the present study, were fore, the present author feels that a subdivision and supplied from various cutting factories or gem description of the samples according to their diag­ collectors in Idar-Oberstein (Figure 24). In all nostic properties is more suitable than a description cases, the country of production was the only according to the producer or producing country. J. Gemm., 1989,21,6 383

In addition, it has to be pointed out that, gure 27), the continuously increasing absorption according to diagnostic properties, only part of the from red to violet is superimposed by several weak samples are easily assigned to a distinct type of and strong absorption bands. These bands are 3+ synthesis as described in Sections II. 4 and II. 6. In assigned to Co (I6) in the case of intense yellow to other cases, some of the observed properties, e.g. intense yellow-orange citrines (type 6, Figure 28). absorption bands in the visible, are not known to This assignment is confirmed by analytical data the present author from literature. Thus, in order to (Table 3). In addition, it was observed that the work out at least some details of the production colour of Co3+- and Fe-containing synthetic citrines processes, trace element analyses were carried out turned blue by heat treatment at 600°C, which is 3+ 2+ using atomic absorption spectroscopy. A general explained by a conversion of Co (I6) to Co (I4) survey of the samples investigated and some of their (Figure 28). In green samples of type 7 a strong 2+ -1 diagnostic properties is given in Table 2, analytical absorption band of Fe (I6) at 13,500 cm is data are presented in Table 3, and absorption observed, which is consistent with literature data spectra are pictured in Figures 25-29. (Figure 29). The absorption spectra of all samples investi­ Several weak absorption bands measured in the gated consist of a strong absorption maximum in spectra of brown, orange-brown, yellow-orange and the ultraviolet, the low energy tail of which extends green samples (Table 2, types 1,2,7, Figures 25,29) to the visible area. In all samples with the exception are in good agreement with literature data of KCl-NaCl-grown synthetic citrine (type 5, Fi­ (Lehmann, 1971a; Khaliov^a/., 1979; cf. Table 1).

Table 2. General survey of synthetic Fe-containing yellow, green and brown quartz investigated, including Fe- and Co-bearing samples designation type 1 type 2 type 3 type 4 type 5 type 6 type 7 country of USA, USSR Japan, USSR Japan, USSR Japan, USSR Japan USA, USSR USSR production colour intense intense intense intense intense intense light green brown or yellow- orange- orange- yellow- yellow or or intense intense orange brown brown orange intense green orange- yellow- brown orange working K2C03 K2C03 K2C03 K2C03 KCl K2C03 K2C03 solution absorption 13,500 maxima (cm"- 1) broad, strong 18,700 20,200 20,200 20,200 21,500 21,500 21,500 22,000 22,000 22,500 23,500 23,500 24,500 24,500 24,800 24,800 24,800 26,500 26,500 26,800 broad, strong 29,000 29,000 optical not not not not not not not twinning observed observed observed observed observed observed observed growth (0001) (0001) (0001) (0001) not (0001) not inhomo- channels || c observed observed genities distorted in­ X-cut and and/or seed terference Y-bar seeds plane figure were used*

*Hosaka and Taki (1983) 384 J.Gemm., 1989,21 ,6

Fig. 24. Colour sequence of synthetic citrines: sample I: type I, produced in USSR; sample 2: type 4, produced in j apan; sample 3: type 4, produced in japan ; sample 4: type 3, prod uced in USSR; sample 5: type 3, produced in USSR; sample 6: type 4, produced in japan (heat­ treated); sample 7: type 6, produced in USA; sample 8: type 3, produced in j apan; 'sample 9: type 6, produced 000 0) in USSR. Size of sample 2 appr ox. II x 14 mm. Photo 00' CD 00 by O. Medenbach, Bochum, FRG.

They are assigned to spin-forbidden transitions of All samples investigated were optically single trival ent iron in interstitial sites of distorted tetra­ crystals (Figure 30) and did not consist of macro­ 3 hedral symmetry, Fe + (14), In contrast, the posi­ scopically twinned or polysynthetically twinned tions of several weak absorption maxima in the individuals on the Brazil law (cf. Figures 4-12). spectra of orange-brown synthetic citrines (Table 2, Only in samples of type 4, an extremely distorted type s 3 and 4, Figure 26) are distinctly shifted and interference figure is observed when the stones arc thus, an assignment of these absorption maxima is viewed parallel to the optical axis (Figures 31-32). rather uncertain. The different spectroscopic pro­ An examination in a direction perpendicular to the perties of various samples are certainly caused by optical axis reveals the presence of fibrous struc­ differing growth conditions. However, without an tures, the fibre axes ofwhich are running parallel to exact knowledge of the compositions of the working the optical axis (Figure 33). Incidentally, liquid and solutions (e.g. concentrations ofK2C03and Fe203), two-phase inclusions are trapped within those chan­ a more detailed interpretation of varying spectro­ nels. Similar fibrous or channel-like structu res scopic pr operties is impossible. An influence of parallel to the c-axis [0001] were mentioned by different oxidizers such as LiN02,LiN03, KMn04 Chadschi and Reschetowa (1975) and Khadzhi and is also assumable (cf. manganese concentrations in Reshetova (1977). These capillary channels penet­ samples of the se particular types , Table 3). rating into the citrine crystals are due to the absence w Vl ~ \0 C"l 00 ...... " 0'- 00 ...... N ':-' J. Gemm., 1989,~ 21, 6 385 2 .-; 2 3 'S « and 700 700 3 15 japan; 3 and 15 Japan;

a-S in c« in USSR. types types 600 in of 600 in USSR. SI'-of S l )

C Pproduced O produced 2 citrines em-I) citrines produced crrr produced 4 500 20 (nm) 4 500 20 (nm) 1000 USSR, ( G ^ I (1000 in synthetic

5^.5 *japan, in USSR, 2 synthetic Japan,

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(8 Ü-in 4_> —« OJ U X u 4 produced

Sspectra a"^ produced

COspectra »-M Q 1 WAVELENGTH 25 WAVELENGTH produced 400 25 produced 400 § 7! a 4: •Ö ^ m3 WAVENUMBER a u •• 3: WAVENUMBER n arn type type Absorption 4; type 3: 3 Absorption 4; type 4: 1 26. 350 350

sFig. Fig. 26. 30 30 05 I 9!i g; "

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'ucitrines tt cm:t 20

500 1» OO . (nm) 20 500 (nrn) USSR; 1000

( G s <*> in (1000 in USSR; type 2: 3 >>-synthetic G CO USSR. synthetic

Oof O GH in « of 3 " «H T3 T3in USSR. produced produced Sispectra l spectra 1,2 WAVELENGTH B^S produced 400 WAVELENGTH 25 .2 •• °« produced 400 1: 25 a^ "*4 4 WAVENUMBER

WAVENUMBER o a c type Absorption 2; J &g.japan, Absorption 2; type 1: 1,2 < cJapan, 25. 350

350 db Fig. Fig. 25. 30 05 ]0 I (:J 9!i <: g; "

WAVELENGTH (nm)

350 400 500 600 700

~ <: g~ ~ '<{ I05

30 25 20 15 WAVENUMBER (1000 crrr t )

Fig. 27. Absorption spectra of synthetic citrine oftype 5 produced in Japan.

of lithium nitrates or nitrites in growth media, citrines. However,it has to be mentioned, that some which form hardly soluble silicates, e.g. eucryptite, faceted synthetic citrines were cut from samples and purify the solution from aluminium. Due to the which were obviously grown under homogeneous paper of Sato (1986), the channel-like structures conditions and, therefore, the samples do not parallel to the optic axis are also observable using display any growth inhomogenities in the gem laser tomography. microscope. These observations are consistent with According to microscopic examinations all sam­ the literature dealing with crystal growth of synthe­ ples of synthetic Fe-bearing citrine with the excep­ tic citrines (cf. Sections 11.4and 11.6). tion of type 5 and possibly some samples of type 7 are grown from basal seeds and thus reveal more or Only occasionally, solid state inclusions in the less pronounced growth structures and colour form of the so-called breadcrumb inclusions are zoning parallel to the basal plane (0001)(Figure 34). observable in synthetic citrine (Figure 35). In Growth structures parallel to the basal pinacoid are stones of type 6, needle-like inclusions which are not observed in natural citrine and natural heat­ orientated parallel to the optical axis are rarely treated amethyst and, thus, basal growth structures found. Feathers consisting of liquid and two-phase and colour zoning unequivocally indicate synthetic inclusions are also very rare.

Table 3. Chemical data of synthetic Fe-containing yellow and brown quartz investigated, including Fe- and Co-bearing samples (in ppm) designation type 1 type 2 type 3 type 4 type 5 type 6 country of USA Japan USSR Japan USSR Japan USA USSR production colour intense intense intense intense intense intense intense brown yellow- orange- orange- yellow- yellow- yellow orange brown brown orange orange Na <10 < 10 < 10 <10 <10 <10 <10 <10 <10 K 354 777 376 460 1045 694 150 1120 935 Fe 1850 1350 455 580 870 1160 2830 960 880 Co < 10 < 10 <10 <10 <10 <10 < )0 130 60 Mn 16 17 36 33 64 87 29 5 5 J. Gemm., 1989,21,6 387

WAVELENGTH (nm)

350 400 500 600 700

~ ~ ~

2 "'t~

3

I 05 4

30 25 20 IS WAVENUMBER (1000 crrr t )

Fig. 28. Absorption spectra of synthetic citrines of type 6; samples in the as-received form: 1produced in USSR, 2 produced in USA; samples converted to a blue colour by heat treatment: 3 originally sample 1,4 originally sample 2.

WAVELENGTH (rim) 350 400 500 600 700

~ <: g~ ~ "<{ I Q5

30 25 20 '5 WAVENUMBER (7000 crrr l )

Fig. 29. Absorption spectrum of synthetic prasiolite of type 7 produced in USSR. 388 J. Gemm.,1989,21,6

Fig. 30. Synthetic citrine of type 3 produced in Japan; interfer­ Fig. 31. Synthetic citrine of type 4 produced in Japan; highly ence figure of an optically untwinned crystal. Crossed distorted interference figure. Crossed polarizers. 18x. polarizers. 14x.

Ti^ 3? Svnthcti citrine lt\pe4pr duced in Japan highlv Pig 33 Svnthetic citrine f tvpt 4 prt duttd in Japan fibrous distorted interference ligure. Crossed polarizers. 35x. structures running parallel to the optic axis. 16x.

Fig. 34. Synthetic citrine of type 3 produced in USSR; growth I i£, 35 Svnthetic titnne t untrv f pr dutti n unkn wn planes parallel to the basal pinacoid. 22x. breadcrumb inclusions. 35x. J. Gemm., 1989,21,6 389

III. 2.6 ARTIFICIALLY-IRRADIATED SYNTHETIC CIT­ iron-containing citrine, channel-like structures RINE (ORIGINALLY COLOURLESS) parallel to the optic axis are found. In addition, Though distinct types of colourless synthetic these samples reveal highly distorted interference quartz turn yellow or greenish-yellow by irradiation figures. treatment (cf. Section II. 5), no irradiation-treated The absorption spectra of all types of iron- synthetic citrine of known origin was commercially bearing synthetic citrine consist of an absorption available. However, two samples submitted for maximum in the ultraviolet, the low energy tail of investigation were possibly of this type. The green­ which causes an increasing absorption from red to ish-yellow faceted stones, 63.7 and 88.8 carats in violet in the visible range. The spectra of all five weight, were internally flawless and without any types of synthetic iron-bearing citrine and synthetic optical twinning or growth structure of diagnostic green quartz, which are grown from K2C03- value. The absorption spectra consisted of an containing solutions with or without additional absorption maximum in the ultraviolet, the low oxidizers (e.g. LiN02, LiN03, KMn04) are super­ energy tail of which extended to the visible. This imposed by a number of weak absorption bands, increasing absorption was superimposed by two which are not found in natural Fe-bearing citrines. -1 Fe- and Co-containing synthetic citrines have a absorption bands at about 15,000 and 26,000 cm -1 (667 and 385 nm). All these data are assumed to be strong absorption band at about 26,800 cm (373 found in both, natural and synthetic irradiation- nm). Only the absorption spectra of synthetic treated yellowish-green citrines. By chemical inves­ citrines, which are grown from KCl-NaCl-bearing tigations using energy-dispersive X-ray fluoresc­ solutions are identical with the spectra of heat- ence analysis, the presence of distinct amounts of treated natural amethyst. Samples of this type of Ge was proved. Though not unequivocal, this result synthetic citrine, which are not yet grown commer­ can be assumed as an important hint towards cially, however, do not display the microscopic Ge-containing synthetic quartz, which was irradia­ characteristics of heat-treated natural amethyst. tion-treated (and possibly annealed subsequently) Natural non-heat-treated, non-artificially- in order to produce a greenish-yellow coloration (cf. irradiated citrines, which are also used in the gem Section II. 5). trade, are often macroscopically twinned and have growth structures parallel to the major and minor rhombohedron as well as parallel to the hexagonal IV Discussion prism. The absorption spectra consist only of an All types of natural and synthetic citrine, which intense maximum in the ultraviolet, the low energy are found on the gem market, reveal a number of tail of which extends to the visible. The citrine characteristic features which are useful for diagnos­ colour centre is completely destroyed by heat tic purposes. Combinations of spectroscopy in the treatment up to 450-550°C and cannot be restored visible and ultraviolet and microscopic investiga­ by subsequent gamma or neutron irradiation. At tions are suggested for the determination of citrines present, this type of citrine has not yet been grown of unknown origin. synthetically. Natural iron-bearing citrines and prasiolites, The thermal stability of artificially-irradiated which are produced from natural amethyst by heat (and in some cases subsequently heat-treated) natu­ treatment, are polysynthetically twinned on the ral quartz is lower than the thermal stability of Brazil law or display a distinct pattern of parallel artificially untreated citrine. A complete bleaching striations, the orientation of which corresponds to of this type of greenish-yellow citrine colour centres the respective growth sector which they are con­ is observed up to 350°C or, in most samples, even at fined to. Colour zoning and growth structures are lower temperatures, and the colour centres are dominant on faces parallel to the major and minor restored by subsequent irradiation. The absorption rhombohedron, r and z, forming characteristic spectra of this third type of citrine are characterized angles of 94°, 134° and 76°. Absorption spectra by an absorption in the ultraviolet, the low energy consist of one strong maximum in the ultraviolet, tail of which extends to the visible. This absorption the low energy tail of which extends to the visible, is superimposed by two bands at about 15,500 and and one single weak absorption band at 21,000 26,000 cm"1 (645 and 385 nm). cm _1 (476 nm). In prasiolites, an additional band at -1 In the literature this type of citrine coloration is about 13,500 cm (741 nm) is found. also described for synthetic quartz, which was All types of synthetic iron-containing citrine and artificially irradiated. However, it was not con­ green quartz are characterized by the absence of firmed experimentally that samples of this type are polysynthetic twinning on the Brazil law and the found in the trade and no information about this is lack of orientated striations. Frequently, dominant available to the present author. Due to the fact that a growth structures parallel to the seed plane (0001) large amount of low costing natural quartz, e.g. are observable. In one distinct type of synthetic from Brazil, is converted to a greenish-yellow 393900 JJ.. Gemm.Gemm.,, 19891989,21,6, 21, 6

coloratiocolorationn bbyy irradiationirradiation,, nnoo necessitnecessityy existexistss ttoo ususee CrowningshieldCrowningshield,, R.R.,, HurlbutHurlbut,, C.c.,, FryerFryer,, C.W.C.W,, 19861986.. A simplsimplee mormoree expensivexpensivee synthetisyntheticc colourlescolourlesss quartquartzz samplesampless procedurproceduree ttoo separatseparatee naturanaturall frofromm synthetisyntheticc amethysamethystt oonn ththee basibasiss ooftwinning.f twinning. Gems and Gemology, 2222,, 130-9130-9.. foforr ththee productioproductionn ooff greenish-yellogreenish-yelloww quartquartzz bbyy ElwellElwell,, D.D.,, 19791979.. Man-made gemstones.gemstones. ElliElliss HorwooHorwoodd Limited,Limited, irradiatioirradiationn treatment.treatment. ChichesterChichester.. IInn alalll typetypess ooff naturanaturall oorr synthetisyntheticc citrinecitrine,, ththee FrondelFrondel,, C.C.,, 19621962.. Dana's System of Mineralogy, Vol. III,III, Silica presencpresencee ooff typicatypicall solisolidd statstatee inclusionsinclusions,, e.ge.g.. FeFe­- Minerals, SeventSeventhh EditionEdition.. WileyWiley,, NeNeww YorkYork.. Gordienko, L.A., L.A., Luchnikov, Luchnikov, V.G., V.G., Samoilovich, Samoilovich, M.I., Khadzhi,M.l., Khad­ oxideoxidess oorr Fe-hydroxideFe-hydroxidess iinn heat-treateheat-treatedd naturanaturall zhi, V.E.V.E.,, TsinoberTsinober,, L.I.L.l.,, TsyganovTsyganov,, E.M.E.M.,, 19691969.. SynthesisSynthesis amethystamethyst,, mineraminerall inclusioninclusionss iinn naturanaturall untreateduntreated ooff colorecoloredd quartzquartz.. Growth of Crystals (Rost Kristallov), 77,, citrincitrinee anandd breadcrumbreadcrumbb inclusioninclusionss iinn syntheticsynthetic 297-300. citrincitrinee mamayy givgivee additionaadditionall informatioinformationn abouaboutt ththee HavenHaven,, Y.Y.,, KatsKats,, A.A.,, vavann WjeringenWjeringen,, J.S.J.S.,, 19661966.. OpticalOptical absorptioabsorptionn anandd paramagnetiparamagneticc resonancresonancee ooff coloucolourr centrecentress iinn naturnaturee ooff ththee samplesample.. ThThee presencpresencee oorr absencabsencee ooff X-rayeX-rayedd ex-quartzα-quartz containincontainingg germaniumgermanium.. Philips Res.Res. healinhealingg fissurefIssuress oorr fingerprinfmgerprintt patternpatternss ooff liquiliquidd oorr Repts, 2121,, 446-76446-76.. two-phastwo-phasee inclusionsinclusions,, howeverhowever,, iiss ooff nnoo diagnosticdiagnostic HosakaHosaka,, M.M.,, TakiTaki,, S.S.,, 19831983.. HydrothermaHydrothermall growtgrowthh ooff amethystamethyst valuevalue.. anandd citrincitrinee iinn NaCNaCIl anandd KCKCIl solutionssolutions.J.. J. Cryst. Growth, 64,64, 572-6572-6.. HuttonHutton,, D.R.D.R.,, 19741974.. DefectDefectss iinn ththee colourecolouredd varietievarietiess ooff quartz.quartz. AcknowledgementAcknowledgementss J. Gemm., 1414,, 156-66156-66.. NumerouNumerouss samplesampless ooff naturanaturall anandd syntheticsynthetic HuttonHutton,, D.R.D.R.,, TroupTroup,, G.J.G.J.,, 19661966.. ParamagnetiParamagneticc resonanceresonance citrinecitrine,, whicwhichh werweree investigateinvestigatedd iinn thithiss paperpaper,, werweree centrecentress iinn amethysamethystt anandd citrincitrinee quartzquartz.. Nature, 211211,, 621.621. KhadzhiKhadzhi,, V.E.V.E.,, ReshetovaReshetova,, G.V.G.V.,, 19771977.. Method of producing kindlkindlyy suppliesuppliedd bbyy differendifferentt firmfIrmss iinn ththee gegemm tradtradee citrine crystals. UniteUnitedd StateStatess PatenPatentt 4,024,0134,024,013.. aass welwelll aass bbyy privatprivatee collectorscollectors.. ThThee authoauthorr isis KhaliovKhaliov,, V.Kh.V.Kh.,, PivovarovPivovarov,, S.S.S.S.,, ZakharovZakharov,, V.K.V.K.,, BokinBokin,, N.M.,N.M., gratefugratefull ttoo ththee followingfollowing personpersonss oorr fIrmsfirms includingincluding ProkhorovaProkhorova,, T.I.T.l.,, KlimashinaKlimashina,, E.V.E.V.,, GorovayaGorovaya,, B.S.B.S.,, 19791979.. ProfProf.. DrDr.. HH.. BankBank,, GebrGebr.. BankBank,, RR.. DröschelDroschel,, E.E. AbsorptioAbsorptionn spectrspectraa anandd structurastructurall statstatee ooff FeFe3+3+ ioionn inin GeorgGeorg,, W. HaagHaag,, GebrGebr.. LeyserLeyser,, ThTh.. LindLind,, JJ.. Ph.Ph. vitreouvitreouss silicassilicas.. Sov.Sov.J. J. Glass Phys. Chem., 44,155-9., 155-9. LehmannLehmann,, G.G.,, 1967.1967. FarbzentreFarbzentrenn dedess EisenEisenss alalss UrsachUrsachee derder WildWild,, alalll ooff Idar-ObersteinIdar-Oberstein,, FRGFRG,, DrDr.. HH.. AA.. HiinniHänni FarbFarbee vovonn AmethystAmethyst.. ZZ.. Naturforschg., 22a22a,, 2080-52080-5.. ooff BaselBasel,, SwitzerlandSwitzerland,, anandd GG.. BossharBosshartt ooff Zurich,Zürich, Lehmann, G., G., 1969. 1969. Interstitial Interstitial incorporation incorporation of di- ofand di- trivalentand triva­ SwitzerlandSwitzerland.. GeGemm materialmaterialss whicwhichh werweree nonott availavail­­ cobaltlent in cobaltquartz. inJ. quartz.J.Phys. Chem. Phys. Solids, Chern. 30, 395-9. Solids, 30, 395-9. ablablee iinn ththee gegemm tradtradee werweree kindlkindlyy givegivenn bbyy ProProf.f Dr.Dr. LehmannLehmann,, G.G.,, 1971a.1971a. YelloYelloww colocolorr centercenterss iinn naturanaturall andand G. Lehmann of Münster, FRG, and Prof. Dr. S. synthetisyntheticc quartzquartz.. Phys. kondens. Materie, 13,297-306.13, 297-306. G. Lehmann of Munster, FRG, and Prof. Dr. S. LehmannLehmann,, G.G.,, 1971b1971b.. ThThee structurstructuree ooff yelloyelloww iroironn centrecentress inin TakiTaki,, DrDr.. MM.. HosakHosakaa ooff KofuKofu,, JapanJapan.. MrsMrs.. M.M. quartzquartz.. Phys. Stat. Sol., (b)(b),, 4848,, K65-K67.K65-K67. VysocanskVysocanskii translatetranslatedd ththee originaoriginall literaturliteraturee fromfrom LehmannLehmann,, G.G.,, 1977.1977. ÜbeUberr didiee FärbungsursacheFiirbungsursachenn natiirlichernatürlicher RussiaRussiann languagelanguage.. FinanciaFinanciall supportsupport was givegivenn bbyy CitrineCitrine.. Z. Dt. Gemmol. Ges., 2626,, 53-6053-60.. grants of the Wirtschaftsministerium des Landes LehmannLehmann,, G.G.,, 1978a.1978a. FestkörperphotochemiFestkorperphotochemiee - eineeine MethodeMethode grants of the Wirtschaftsministerium des Landes zurzur ErzeugungErzeugung ungewiihnlicherungewöhnlicher Wertigkeitsstufen.Wertigkeitsstufen. Angew.Angew. Rheinland-Pfalz,Rheinland-Pfalz, FRG.FRG. Chem., 90,90, 95-10395-103.. Lehmann,Lehmann, G.,G., 1978b.1978b. FarbenFarben vovonn MineralenMineralen undund ihreihre Ursachen.Ursachen. ReferencesReferences Fortschr. Miner.,Miner., 56,56, 172-252.172-252. Lehmann,Lehmann, G.,G., 1981.1981. Farbzentren in Mineralen und synthetischen Balakirev, V.G.,V.G., Keivlenko, Keivlenko, E.Y., E.Y., Nikolskaya, Nikolskaya, L.V., L.V., Samoilovich, Samoilo­ Kristallen (Forschungsbericht des Landes Nordrhein­Nordrhein- vich, M.l.,M.I., Khadzhi,Khadzhi, V.A.,V.A., TsinoberTsinober,, L.l.,L.I., 1979.1979. MineralogyMineralogy Westfalen; Nr. 3066: Fachgruppe Physik, Chemie, Biologie).Biologie). and crystal physics of gem varieties of silica. NedraNedra,, MoscowMoscow WestdeutscherWestdeutscher Verlag,Verlag, Opladen.Opladen. (in Russian). Lehmann, G., Bambauer, H.U., 1973. Quarzkristalle und ihre Balitsky,Balitsky, V.S.,V.S., 1981.1981. GemmologyGemmology ofof somesome colourecolouredd syntheticsynthetic Lehmann, G., Bambauer, H.U., 1973. Quarzkristalle und ihre quartz.J.quartz. J. Gemmol. Soc. Japan, 8,8, 103-17.103-17. Farben.Farben. Angew. Chem., 85,85, 281-9281-9.. Lehmann,Lehmann, G.,G., MooreMoore,, W.J.WJ.,, 1966.1966. OpticalOptical andand paramagneticparamagnetic Balitsky, V.S.,V.S., Balitskaya, Balitskaya, O.V., O.V., 1985. 1985. Dichromatic Dichromatic amethyst-citrine amethyst­ propertiesproperties ofof ironiron centerscenters inin quartz.quartz. J. Chem. Phys., 44,44, citrine quartzquartz andand genesisgenesis conditionsconditions ofof it.it. Zap. Vses. 1741-5.1741-5. Mineral. Obsh.,Obsh., 114 114,664-76, 664-76 (in (in Russian). Russian). Balitsky,Balitsky, V.S.,V.S., Balitskaya,Balitskaya, O.V.,O.V., 1986.1986. TheThe amethyst-citrineamethyst-citrine Lind, Th., Th., Schmetzer, Schmetzer, K., 1982.K., Infrarotspektroskopie1982. Infrarotspektroskopie geschliffener ge­ dichromatism in in quartz quartz and and its origin.its origin. Phys. Phys. Chem. Chem. Minerals, Miner­ schliffener Edelsteine,Edelsteine, dargestelltdargestellt amam BeispielBeispiel vonvon echtenechten 13, 415-21.als, 13,415-21. undund synthetischensynthetischen Amethysten.Amethysten. Z. Dt. Gemmol. Ges., 3131,, Balitskii, V.S., V.S., Samoilovich, Samoilovich, M.I., M.l., Tsinober, Tsinober, L.I., L.l.,1970. 1970.Tungsten Tung­ 143-50. sten andand galliumgallium asas structuralstructural impuritiesimpurities inin syntheticsynthetic quartzquartz Lind,Lind, Th.,Th., Schmetzer,Schmetzer, K.,K., 1983.1983. A methodmethod forfor measuringmeasuring thethe crystals. Sov. Sov. Phys.-Dokl., Phys.-Dokl., 15 ,15,210-12. 210-12. infraredinfrared spectraspectra ofof facetedfaceted gemsgems suchsuch asas naturalnatural andand Ballman,Ballman, A.A.,A.A., 1961.1961. TheThe growthgrowth andand propertiesproperties ofof coloredcolored syntheticsynthetic amethysts.J.amethysts. J. Gemm., 18,411-20.18, 411-20. quartz.quartz. Amer. Mineral., 46,46, 439-46.439-46. Lind,Lind, Th.,Th., Schmetzer,Schmetzer, K.,K., 1985.1985. NeueNeue UntersuchungenUntersuchungen anan inin Bank,Bank, H.,H., 1976.1976. Citrin.Citrin. Z.Z. Dt. Gemmol. Ges., 25,189-94.25, 189-94. JapanJapan hergestelltenhergestellten synthetischensynthetischen Amethysten.Amethysten. Z. Dt.Dt. Bukanov,Bukanov, V.V.,V.V., Markova,Markova, G.A.,G.A., 1969.1969. TheThe smokysmoky andand citrinecitrine Gemmol. Ges., 34,34, 160-4.160-4. colorcolor ofof naturalnatural quartz.quartz. Dokl. Akad. Nauk SSSR, EarthEarth Lind, Th.,Th., Schmetzer, Schmetzer, K., K., 1987. 1987. New New investigations investigations of synthetic ofsynthe­ Science Sections, 187,187, 115-17.115-17. amethyststic amethysts produced produced in Japan. J.in Gemm.,Japan.J. 20 ,Gemm., 274-7. 20, 274-7. Chadschi, W.E., WE., Reschetowa, Reschetowa, G.W., G. W, 1975. 1975. Verfahren Verfahren zur zur Herstellung H erstel­ Lind, Th.,Th., Schmetzer, Schmetzer, K., Bank,K., Bank, H., 1983. H., Untersuchungsmethoden1983. Untersuchungs­ lung von Zitrinkristallen. Offenlegungsschrift,Offenlegungsschrift, 2401106,2401106, zur Unterscheidungmethoden zur vonUnterscheidung natürlichen und von synthetischen natiirlichen und syn­ Deutsches Patentamt. Patentamt. Amethysten.thetischen Z. Dt.Amethysten. Gemmol. Ges., Z. Dr. 32 ,Gemmol. 126-37. Ges., 32, 126-37. Chentsova,Chentsova,L.G.,Butuzov, L.G., Butuzov, V.P., V.P., 1962. 1962. Smoky Smoky color color and and thermoluminescence thermo­ Lind,Lind , Th.,Th., Schmetzer,Schmetzer, K.,K., Bank,Bank, H.,H., 1985.1985. MethodsMethods forfor thethe luminescence ofof X-rayedX-rayed syntheticsynthetic quartzquartz containingcontaining tracestraces distinction of of natural natural and and synthetic synthetic amethysts. amethysts. Aust. Aust.Gemmol., Gem­ ofof Li,Li, NaNa andand Ge.Ge. Growth of Crystals (Rost(Rost Kristallov), 3,3, 15, 462-70.mol., 15,462-70. 336-9. Maschmeyer,Maschmeyer, D.,D., Lehmann,Lehmann, G.,G., 1983.1983. NewNew holehole centerscenters inin J.J. Gernrn.,Gemm.,1989,21, 1989,21,66 391391

naturalnatural quartz.quartz. Phys. Chem. Minerals, 10,10, 84-8.84-8. Schmetzer,Schmetzer, K.,K., 1986.1986. AnAn improvedimproved samplesample holderholder andand itsits useuse inin Maschmeyer,Maschmeyer, D.,D., Lehmann,Lehmann, G.,G., 1984.1984. NewNew electronelectron centerscenters inin thethe distinctiondistinction ofof naturalnatural andand syntheticsynthetic rubyruby asas wellwell asas neutron-irradiatedneutron-irradiated naturalnatural quartz.quartz. Solid State Commun., 50,50, naturalnatural andand syntheticsynthetic amethyst.J.amethyst. J. Gemm., 20,20, 20-33.20-33. 1015-18.1015-18. Schmetzer,Schmetzer, K.,K., 1987.1987. MicroscopicMicroscopic observationobservation ofof twinningtwinning Maschmeyer,Maschmeyer, D.,D., Niemann,Niemann, K.,K., Hake,Hake, H.,H., Lehmann,Lehmann, G.,G., microstructuremicrostructure inin naturalnatural amethyst.amethyst. N. JJb. b. Miner. MMh., h., Rauber,Räuber, A.,A., 1980.1980. TwoTwo modifiedmodified smokysmoky quartzquartz centerscenters inin 1987,8-15.1987, 8-15. naturalnatural citrine.citrine. Phys. Chem. Minerals, 6,145-56.6, 145-56. Schmetzer,Schmetzer, K.,K., 1988.1988. ThermalThermal stabilitystability ofof yellowyellow colourcolour andand McLaren,McLaren, A.C.,A.C., Pitkethly,Pitkethly, D.R.,D.R., 1982.1982. TheThe twinningtwinning micro­micro- colourcolour centrescentres inin naturalnatural citrine.citrine. N. Jb. Miner. Mh., volvol structurestructure andand growthgrowth ofof amethystamethyst quartz.quartz. Phys. Chem.Chem. 1988,1988, 71-80.71-80. Minerals, 8,8, 128-128-3535. . Schmetzer, K., K., Bank, Bank, H., 1980.H., 1980. Zur Unterscheidung Zur Unterscheidung natürlicher natiir­ Nassau,Nassau, K.,K., 1977.1977. AnmerkungAnmerkung zuzu 'iiber'über diedie FarbungsursachenFärbungsursachen licher undund synthetischersynthetischer Amethyste.Amethyste. Z. Dt. Gemmol. Ges.,Ges., NatiirlicherNatürlicher Citrine'Citrine' inin Z. Dt. Gemmol. Ges., 2626 (1977)(1977) 29,17-19.29, 17-19. 53-60.53-60. Z. Dt. Gemmol. Ges., 26,26, 222.222. Schneider, W.L., w.L., Dröschel, Droschel, R., R., 1983. 1983. Beobachtungen Beobachtungen an polysynthetisch an poly­ Nassau,Nassau, K.,K., 1980.1980. Gems made by man. ChiltonChilton BookBook Company,Company, verzwillingtensynthetisch Quarzen verzwillingten - ein Beitrag Quarzen zur Unterscheidung - ein Beitrag zur U nter­ Radnor,Radnor, Pennsylvania.Pennsylvania. scheidung natiirlichernatürlicher undund synthetischersynthetischer Amethyste.Amethyste. Z. Dt.Dt. Nassau,Nassau, K.,K., 1981.1981. ArtificiallyArtificially inducedinduced colorcolor inin amethyst-citrineamethyst-citrine Gemmol. Ges., 3232,, 28-38. 28-38. quartz.quartz. Gems and Gemology, 17,17, 37-9.37-9. Steshchin,Steshchin, V.A.,V.A., 1979a.1979a. Radiation-inducedRadiation-induced colourcolour ofof quartzquartz Nassau,Nassau, K.,K., Prescott,Prescott, B.E.,B.E., 1975.1975. A reinterpretationreinterpretation ofof smokysmoky fromfrom thethe crystal-containingcrystal-containing veinsveins ofof thethe Nagol'novoNagol'novo rangerange quartz.quartz. Phys. Stat. Sol., (a)(a) 29,29, 659-63.659-63. (Donets(Donets CoalCoal Basin).Basin). Vopr. Geokhimii, Mineral., PetrolPetrol.. i Nassau,Nassau, K.,K., Prescott,Prescott, B.E.,B.E., 1977a.1977a. Smoky,Smoky, blue,blue, greenishgreenish Rudoobraz, 1979,30-71979, 30-7 (in(in Russian).Russian). yellow,yellow, and otherand other irradiation-related irradiation-related colors incolors quartz. in quartz.Mineral. Miner­ Steshchin,Steshchin, V.A.,V.A., 1979b.1979b. NewNew typetype ofof citrinecitrine colouringcolouring inin quartz.quartz. al. Mag., 41,41, 301-12.301-12. Vopr. Geokhimii,Geokhimii, Mineral.,Mineral., Petrol.Petrol . i iRudoobraz, Rudoobraz, 1979,1979 ,37-42 37-42 Nassau, K., K., Prescott, Prescott, B.E., B.E., 1977b. 1977b. A uniqueA unique green green quartz. quartz. Amer. Amer. (in(in Russian).Russian). Mineral., 62,62, 589-90.589-90. Stock,Stock, H.D.H.D.,, Lehmann,Lehmann, G.,G., 1977.1977. PhenomenaPhenomena associatedassociated withwith Neumann,Neumann, E.,E., Schmetzer,Schmetzer, K.,K., 1984a.1984a. MechanismMechanism ofof thermalthermal diffusiondiffusion ofof trivalentrivalentt ironiron inin amethystamethyst quartz.quartz. J. Phys.Phys. conversionconversion ooff colourcolour andand colourcolour centrescentres byby heatheat treatmenttreatment ofof Chem. Solids, 38,38, 243-6.243-6. amethyst.amethyst. N.N.Jb. Jb. Miner. Mh., 1984,272-82.1984, 272-82. Sunagawa,Sunagawa, I.,I., 1982.1982. GemGem materials,materials, naturalnatural andand artificial.artificial. In:In: Neumann,Neumann, E.,E., Schmetzer,Schmetzer, K.,K., 1984b.1984b. Farbe,Farbe, FarbursacheFarbursache undund Kaldis,Kaldis, E.E. (Ed.).(Ed.). Current topics in materials science, 1010,, MechanismenMechanismen derder FarbumwandlungFarbumwandlung vonvon Amethyst.Amethyst. Z. Dt.Dt. 353-497.353-497. North-HollandNorth-Holland PublishingPublishing Company,Company, Amsterdam,Amsterdam, Gemmol. Ges., 33,33, 35-42.35-42. NeNeww York,York, Oxford.Oxford. O'Donoghue,O'Donoghue, M.M.,, 1983.1983. Identifying man-made gems. N.A.G.N.A.G. Tsinober,Tsinober, L.I.,L.I., Chentsova,Chentsova, L.G.,L.G., 1959.1959. SyntheticSynthetic amethystamethyst PressPress Ltd.,Ltd., London.London. quartz.quartz. Sov. Phys.-Cryst., 4,4, 593-5593-5.. Samoilovich,Samoilovich, M.I.,M.I., Tsinober,Tsinober, L.I.,L.I., Dunin-Barkovsky,Dunin-Barkovsky, R.L.,R.L., Tsinober,Tsinober, L.I.,L.I., Chentsova,Chentsova, L.G.,L.G., Shternberg,Shternberg, A.A.,A.A., 1959.1959. TheThe Lisitsina,Lisitsina, E.E.,E.E., Khadzhy,Khadzhy, V.E.,V.E., 1976.1976. AboutAbout thethe thirdthird typetype greengreen andand brownbrown colorscolors ofof syntheticsynthetic quartzquartz crystals.crystals. Growth ofof citrinecitrine colourcolour ofof naturalnatural quartz.quartz. Zap. Vses. Mineral.Mineral. of Crystals (Rost Kristallov), 2,2, 45-9.45-9. Obsh., 105,105, 223-7223-7 (in(in Russian).Russian). Tsinober,Tsinober, L.I.,L.I., Samoilovich,Samoilovich, M.I.,M.I., Gordienko,Gordienko, L.A.,L.A., Chentsova,Chentsova, Samoilovich, M.I., M.I., Tsinober, Tsinober, L.I., L.I., Khadzhi, Khadzhi, I.P., 1969a.I.P., 1969a. Investigation Inves­ L.G.,L.G., 1967.1967. AnomalousAnomalous pleochroismpleochroism inin syntheticsynthetic smokysmoky tigationof colored of crystals colored of crystals synthetic of quartz. synthetic Sov. quartz.Phys.- Sov. Phys.­ quartzquartz crystals.crystals. Sov. Phys.-Cryst., 12,12, 53-653-6.. Dokl., 14,14, 6-8.6-8. WildWild,, G.O.G.O.,, 1968.1968. CitrinCitrin-- unundd gelgelbb gebranntegebrannterr AmethystAmethyst,, zwezweii Samoilovich,Samoilovich, M.I.M.I.,, TsinoberTsinober,, L.I.L.I.,, KreiskopKreiskop,, V.N.V.N.,, 1969b.1969b. TheThe verschiedene Quarze. Quarze. In: In:Mackowsky, Mackowsky, M.-T. M.-T. (Ed.) Edelsteine.(Ed.) Edel­ naturnaturee ooff radiation-produceradiation-producedd citrincitrinee coloratiocolorationn iinn quartz.quartz. Aufschlußsteine. Sonderheft, AufschlufJ 18Sonderheft,, 121-6. 18, 121-6. Sov. Phys.-Cryst., 13,626-8.13, 626-8. WoodWood,, D.L.D.L.,, BallmanBallman,, A.A.A.A.,, 1966.1966. BluBluee synthetisyntheticc quartzquartz.. Amer. Sato,Sato, K.K.,, 1986.1986. ObservatioObservationn anandd differentiatiodifferentiationn ooff naturanaturall andand Mineral., 5151,, 216-20216-20.. syntheticsynthetic quartquartzz usinusingg laselaserr tomographytomography.. Aust. Gemmol., 1616,, ZakharovZakharov,, V.K.V.K.,, PivovarovPivovarov,, S.S.S.S.,, KhalilovKhalilov,, V.Kh.V.Kh.,, 1977.1977. TheThe 72-8072-80.. absorptioabsorptionn spectrspectraa ooff ththee FeFe2+2+ ioionn iinn polarizepolarizedd lighlightt anandd itsits SawyerSawyer,, B.B.,, 1974.1974. Color sorting of irradiated quartzquarlZ materials. structurastructurall positiopositionn iinn single-crystasingle-crystall quartquartzz anandd vitreousvitreous UniteUnitedd StatesStates PatenPatentt 3,837,826.3,837,826. silicasilica.. Sov.Sov.J. J. Glass Phys. Chem., 33,, 298-301.298-301. Sawyer,Sawyer, B.B.,, 19761976.. Color sorting of irradiated materials and a Zecchini, P., P., Mérigoux, Merigoux, H., H., 1980. 1980. Étude Etude de l'absorption de I'absorption infrarouge infra­ calibrated color comparison array. UniteUnitedd StatesStates PatentPatent rouge dedess quartquartzz hyalihyalinn eett coloréscolores,, naturelnaturelss oouu ddee synthese:synthèse: 3,936,1883,936,188.. applicatioapplicationn àa llaa gemmologiegemmologie.. C.R. Acad. Sc. Paris, SérieSerie D,D, Schlossin,Schlössin, H.H.H.H.,, LangLang,, A.R.A.R.,, 1965.1965. A studstudyy ooff repeatedrepeated 290,290,291-4. 291-4. twinningtwinning,, latticlatticee imperfectionimperfectionss anandd impuritimpurityy distributiodistributionn inin amethystamethyst.. Phil. Mag., 12,12, 283-96283-96.. Schmetzer,Schmetzer, K.K.,, 1985.1985. EiEinn verbesserteverbesserterr ProbenhalteProbenhalterr unundd seineseine AnwendunAnwendungg auauff ProblemProblemee dederr UnterscheidunUnterscheidungg natiirlichernatürlicher unundd synthetischesynthetischerr RubinRubinee sowisowiee natürlichenatiirlicherr unundd syntheti­syntheti­ [[ManuscriptManuscript received 20 April, 1987, revised 8 December schescherr AmethysteAmethyste.. ZZ.. Dt. Gemmol. Ges., 3434,, 30-4730-47.. 19881988]] 392 J. Gemm., 1989,21,6

Proceedings of the Gemmological Association of Great Britain and Association Notices

OBITUARY copy of the 2nd edition of his Dictionary ofGemmo- Mr Syed Vaqar Ahmad, FGA (D.1970), Lon­ logy to the Association's Chairman, Mr Arthur E. don, died on 23 January 1989. Thomas, FGA. Mr Cecil A. Bond, FGA (D.1964), Ufford, Woodbridge, died on 4 January 1989 after a long MEMBERS' MEETINGS illness. Cecil Bond was the third generation of retail London jewellers known as A.A. Bond & Sons Ltd with On 29 March 1989 at the Flett Theatre, Geologi­ shops at Hoddesdon and Waltham Abbey. He cal Museum, Exhibition Road, South Kensington, retired in 1983 because of ill health. As well as being London SW7, Mr E.A. Jobbins gave an illustrated a Fellow of the Gemmological Association, he was a lecture using the extensive collection of colour craft member of the British Horological Institute transparencies taken by him during his five months and an active member of the National Association of stay in Brazil in 1973 and his one month trip in Goldsmiths. He leaves a widow, Joan, two sons, a 1987. As well as a description of the gemstones daughter and seven grandchildren. found in Brazil, Alan Jobbins explained some of the reasons for their distribution. Mr Ronald C. Stevens, FGA (D. 1970), Howick, Auckland, New Zealand, died on 25 December Midlands Branch 1988. On 20 January 1989 at the Society of Friends, Dr Johnson House, Colmore Circus, Birmingham, Mr GIFTS TO THE ASSOCIATION CR. Burch, Senior Lecturer in Gemmology and The Council of the Assocation is indebted to the Geology at the Sunderland Polytechnic, gave an following for their gifts: illustrated talk on inclusions in natural and synthe­ Mr B. A. Handana of Indonesia for a copy of the tic corundum. book Batu Permata by Rahasia. On 17 February 1989 at the Society of Friends Mr E. Fontana and Mr WL Kunsch of Sao Mr John R. Bugg gave a talk entitled The law and Bernardo do Campo, Brazil, for a copy of their book the gemmologist'. entitled Gems of Brazil. On 17 March 1989 at the Society of Friends, a Dr Dietmar Schwarz of Ouro Preto, Brazil, for a talk was given by Mr Peter Read entitled The >y of his book entitled Esmeraldas - Inclusoes em Brewster Angle refractometer! Mr Read also de­ was. monstrated the new GEMDATA computer program. NEWS OF FELLOWS North West Branch )n 23 November 1988 Mr Peter Read gave two On 18 January 1989 at Church House, Hanover mustrated talks at a Gala Buffet Supper arranged by Street, Liverpool 1, Mr John Pyke displayed and the Gemmological Association of South Africa in gave a talk on his collection of rare and interesting the Sunnyside Park Hotel, Johannesburg. The gemstones. subjects of the two talks were the laser Brewster- On 15 February 1989 Dr J.W Harris, Senior angle refractometer developed by Peter Read, and Lecturer of Strathclyde University, gave a talk on his GEMDATA computer program for gem identi­ diamonds and diamond mining around the world. fication. An experimental Brewster-angle refracto­ meter was demonstrated after the first talk, and an COUNCIL MEETING IBM PC-compatible computer was made available At a meeting of the Council of the Association to show the various features of the GEMDATA held on 28 February 1989 at the Royal Automobile program. After his talks, Peter Read presented a Club, 89 Pall Mall, London SW1, the business J. Gemm., 1989,21,6 393 transacted included the following: (1) the appoint­ Lilly, Gregory R., Taranaki, New Zealand. ment of Mrs Evelyne Stern, FGA, as an Examiner; Lockie, Debra L., Auckland, New Zealand. (2) the election to membership of the following: McDowell, Barry M., Wellington, New Zealand. Matoba, Hiroshi, Nara City, Japan. Fellowship Murata, Michiko, Tokyo, Japan. Bruggeman, Renate F., Almelo, The Netherlands. Naitoh, Yukihiro, Shimizu City, Japan. 1986 Nakane, Tomoko, Tokyo, Japan. Chan, Yuk C, Hong Kong. 1988 Nercessian, Armine, New York, NY, USA. Chan Cheng, Rosalia Y.K., Honolulu, HI, USA. Noyori, Kazuhiko, Fukuoko City, Japan. 1988 O'Reilly, Stan J., Galway, Eire. Collins, Steven J.C., Letchworth. 1988 Ozaki, Keiko, Kawanishi City, Japan. Dabell, Louise C, Nottingham. 1988 Palmer, Guen, Ditchling. Dunn, Wendy S., London. 1987 Pimantip, Nin, London. Franco da Fonseca, Ana L., Sao Paulo, Brazil. 1988 Pine, Irving C, Delray Beach, Fla., USA. Girod, Daniel F., Amsterdam, The Netherlands. Ravindran, Mahaluxmy, Bangkok, Thailand. 1988 Richards, Keith, Epsom. Haufe, Wilfred, Toronto, Ont., Canada. 1988 Safwat, Hanafi, London. Hergel, James E., Toronto, Ont., Canada. 1988 Sarin, R., Arlington, Va., USA. Kuwahara, Chizu, Yokosuka City, Japan. 1988 Sarmiento, Luis, Madrid, Spain. Lewis, David T.K., Nottingham. 1968 Satoh, Mariko, Yokohama City, Japan. Lewis, Rachel, Stockport. 1988 Seymour, Nicola, Hove. McKearney, Michael C, London. 1984 Shimoda, Tetsuhiro, Fukuoka City, Japan. Maharaj, Rajendra K., Toronto, Ont., Canada. 1988 Stanley, Sylvia, Clearwater Bay, Hong Kong. Muff-Somma, Walter C, Muri, Switzerland. 1988 Tachibana, Hirogi, Osaka, Japan. Nakamura, Midori, Ichikawa City, Japan. 1983 Tanaka, Norihiro, Tokyo, Japan. Ng, Siu K., Hong Kong. 1987 Tanzawa, Megumi, Nakacoma-Gun, Japan. Potts, James D., Telford. 1988 Tay, Thye S., Singapore. Sumar, Nizarali P., Nairobi, Kenya. 1988 Themelis, Ted., Clearwater, Fla., USA. Wedekind, Kenneth J., Wakefield. Ordinary Membership Wilson, Mathew D., Broadstairs. Aoki, Kazuo, Fujisawa City, Japan. Woods, Janina, Warwick» Candela, Conchita, Bari, Italy. Yasuda, Jun, Tokyo, Japan. Chang, Kuei Y, Taipei, Taiwan. Yutani, Atsuko, Osaka, Japan. Chowdhary, Kawaljit, Wembley. Christof!, Christiana, Limassol, Cyprus. Costa, L.R., London. GEMMOLOGICAL ASSOCIATION OF Desor, Manmohan, Leicester. ISRAEL Fernando, Joseph S., Colombo, Sri Lanka. The formation of this new organization has just Fogarty, Jolyan L., Jackson, Wyo., USA. been announced. The address is 1 Japotinsky Girardi, Josephine C, Hong Kong. Street, Ramat-Gan, 52520 Israel. Grigoriadis, Giorgios D., Athens, Greece. Hainovitz, Jonathan, Jerusalem, Israel. FORTHCOMING MEETINGS Hare, Rebecca, London. The 1989 Annual General Meeting of the Asso­ Hayakawa, Taketoshi, Chigasaki City, Japan. ciation is to be held on 12 July 1989 at the Flett Hill, Linda S., Jakarta, Indonesia. Theatre, Geological Museum, Exhibition Road, Holt, Dorothy O., London. South Kensington, London SW7. This will be Hughes, David J., Cardiff. followed by a Gemmological Forum similar to those Itoyama, Mariko, Nagasaki City, Japan. held in previous years that have proved so suc­ Jhaveri, Devang, London. cessful. Johns, Alan T., Perranporth. Kammerling, Robert C, Santa Monica, Calif., USA. Kapur, Sharad, New Delhi, India. Knudson, Eric, London. Komai, Rie, Kawaguchi City, Japan. Kuinose, Masafumi, Wakayama City, Japan. Leadbetter, Bibette, Skelmersdale. 394 J. Gemm., 1989,21,6

Letters to the Editor

From Rudolf Voll From Kenneth Scarratt, FGA

Dear Sir, Dear Sir, As a gem tester, Mr Kenneth Scarratt fails to RE: LETTER FROM MR RUDOLF VOLL divulge the cause of double-nucleated cultured I have often written items into 'Notes from the pearls from the Pinctada martensii oyster (Notes Laboratory' in the hope that someone with a close from the Laboratory-13, Journal ofGemmology, 21, knowledge ofthat particular area of our subject will 5, 294); let me advise readers that there was no write to the Editor with additional information. attempt whatsoever to create 'twins', but that, This, however, and somewhat disappointingly, very decades ago, the technique that prevented the seldom occurs. I was therefore very pleased to read undesired joining of large nuclei inside the gonad Mr VolPs comments on the double-nucleated cul­ was insufficiently developed. tured pearls. But today it is well-nigh impossible to find one Mr Voll is correct in assuming that his contribu­ twin among many 'kan' (käme) of cultured pearls. tion would be well received; one only wishes that Kan is an ancient Chinese weight unit of 3.75kg or there were more people in the gemstone industry 1000 momme, which was outlawed for general use who would put pen to paper and let us read of their in Japan in 1960 and is, by special licence, only experiences within these pages. permitted to be used by the pearl industry. Twins' still occur today in the 2-3 mm nuclei but they are usually cut apart and used as pearls for Yours etc., 'trimming' or 'paving' purposes, having a practical Kenneth Scarratt near-half-pearl shape after separating. The 'hollow' cultured pearls are a phenomenon which happened mainly in the freshwater mollusc 24 February 1989 Hyriopsis schlegeli in Lake Biwa. Because of the The Gem Testing Laboratory of Great Britain, pearl-'unlike' weight and especially the usually 27 Greville Street, London EC1N 8SU. 'dried prune' surface, cultivation has been discon­ tinued. My daughter Aloha, a 1981 winner of the Ander­ son Medal and student of Mrs Anne Paul's class, lives now in Bangkok, but I read the Journal which still arrives in Hong Kong, and I believe that you do not object to my co-operation on her behalf, believing to be competent enough as the only active non-Japanese member at the monthly Tokyo pearl auctions. I have specialized in cultured pearls since 1938 in Tokyo, but spend two weeks of every month in Hong Kong.

Yours etc., Rudolf Voll

14 February 1989 C-6, 15 Fl., Hankow Centre, 1 Middle Road, Kowloon, Hong Kong. J. Gemm., 1989,21,6 395

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Have you a worn prism? ADVERTISING IN Arrangements have now been made to THE JOURNAL OF offer a speedy repair/overhaul service for Rayner refractometers*. GEMMOLOGY So if your refractometer glass prism is cracked, chipped or marked, or the The Editors of the Journal invite refractometer just is not operating advertisements from gemstone satisfactorily, simply send it to and mineral dealers, scientific the Gemmological Association for instrument makers, publishers overhaul. This will include completely stripping the unit down, checking and and others with interests in the replacing, if necessary, damaged internal gemmological, mineralogical, lens system parts, replacing the top glass lapidary and jewellery fields. prism with a harder glass and generally cleaning and realigning optics to Rates per insertion, excluding ensure many more years of use. VAT, are as follows: Whole page Half page Quarter page The cost is just £62.50 plus postage and £180 £100 £60 VAT where applicable. Gemmological Association of Enquiries to Mrs M. Burland, Great Britain, Saint Dunstan's House, Advertising Manager, Carey Lane, London EC2V 8AB. Gemmological Association, Saint Dunstan's House, * Please note that it is not possible to repair some of the old Carey Lane, London EC2V 8AB. 'black style' refractometers as they are now obsolete. 398 J. Gemm., 1989,21,6

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R.M.Weare R. HOLT & CO. LTD. & Company Limited. 98 Hatton Garden, London ECIN 8NX 67 The Mount York. England. Y02 2AX. Telephone 0904-621984. Telex: 57697 Yorvex.G Telephone 01-405 0I97/5286 Telex 2I879 Minholt St a£ GEMDATA A computer program for gem identification The GEMDATA Package by Peter Read (see p. 338 for full details) is available through the Gemmological Association at £84.00 plus postage, packing and VAT* (*UK only at £12.60). Postal rates are as follows: £3.50, UK and Eire; £4.00 Europe; £6.00 rest of the world. To order your Package use the form below.

To: Gemmological Association of Great Britain, Saint Dunstan's House, Carey Lane, London EC2V8AB. Please supply copies of the GEMDATA package. *I use a colour/ monochrome monitor *I enclose remittance £ /debit my credit/charge card (please tick appropriate box) • £3 • gg • ggg • Diners Club Card No Expiry date Name Address Telephone No.. Signature Date. *Delete as applicable J. Gemm., 1989,21,6 399

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FGAMOCK LJvuAtojme/i «Jv. K^aAeu, F.G.A. PRACTICALS Dealer in fine, rare and collectors' Two two-day residential courses gemstones, carvings and mineral specimens. Full practical examination work-outs Specialist supplier of jade, from Alan Hodgkinson lecture team archaic nephrite to imperial jadeite. Upton Hall, Newark, Notts. Valuations of collections and of Two 3V2 hours morning individual items undertaken. practical examinations, I wish to purchase gem and mineral two afternoons plus full evening collections, engraved gemstones Instruments, methods and techniques (especially intaglios) and old books All syllabus gems and crystals on gem related subjects. Christopher R. Cavey, F.G.A. 6-7 June and 8-9 June Bond Street Antique Centre, 124 New Bond St., London W.l. Contact Retail Jeweller; 100 Avenue Road London NW3 3TP Telephone: 01-495 1743 Telephone: 01-935 6611 400 J. Gemm., 1989,21,6

M K WEISS LTD Manufacturing Goldsmiths Beautiful Hand-Made Solid Gold Loupes in 9ct and 18ct with 10X aplanatic and achromatic triplet 15mm lenses. Large selection of surface finishes or plain polished, and supplied in soft leather pouches. Available only from K WEISS LTD 9-10 Charterhouse Buildings Goswell Road London EC1M7AN Telephone: 01-251 0123 Fax:01-253 9695 Telex: 94012208 (WEIS G)

ATTENTION: enests Museums, Educational * Leaders in gemmological education, specializing Establishments in intensive tuition, from scratch to F.G. A. Diploma in nine months. We can claim a very & Collectors high level of passes including Distinctions I have what is probably the largest amongst our students. * We organize a comprehensive programme of range of genuinely rare gemstones in Study Tours for the student and practising the UK - from Apophyllite to gemmologist, to areas of gemmological interest, including Antwerp, Idar-Oberstein, Sri Lanka Zincite. Also rare synthetics, i.e. and Bangkok. Scheelite, Bismuth Germanate, • Dealers in gemstones and rare specimens for Knischka rubies and a range of both the student and the collector. Inamori. • Suppliers of gemmological instruments, especially the world famous OPL diffraction Lists available- grating spectroscope, together with a range of (large s.a.e. appreciated) books and study aids. For further details of these and other activities, please A.J. FRENCH F.G.A. contact:- Colin Winter, F.G.A., or Hilary Taylor, B.A., Gem Dealer & Consultant F.G.A., at GENESIS, 21 West Street, Epsom, 82 Brookley Road Surrey KT18 7RL, England. Brockenhurst, Hants S042 7RA Tel: Epsom (03727) 42974. Telephone: 0590 23214 Telex: 923492 TRFRT G attn GENS. GEMMOLOGICAL ASSOCIATION OF GREAT BRITAIN

The Anns and Crest of the octahedra and the gem-set ring Association, conferred by a grant indicates the use of gems in of Arms made by the Kings of ornamentation. The lynx ofthe Arms under royal authority. crest at the top was credited, in The cross is a variation of that ancient times, with being able to in the Arms ofthe National see through opaque substances. Association of Goldsmiths of He represents the lapidary and Great Britain and Ireland. In the student scrutinizing every the middle is a gold jewelled aspect of gemmology. In the book representing the study of paws is one of the oldest heraldic gemmology and the emblems, an escarbuncle, to examination work ofthe represent a very brilliant jewel, Association. Above it is a top usually a ruby. The radiating arms plan of a rose-cut diamond inside suggest light diffused by the a ring, suggesting the scrutiny of escarbnncle and their tips are shown gems by magnification under a lens. as jewels representing the colours of The lozenges represent uncut the spectrum.

Historical Note The Gemmological Association of Great Canadian Gemmological Association, the Gem Britain was originally founded in 1908 as the and Mineral Society of Zimbabwe, the Education Committee of the National Gemmological Association of Hong Kong, the Association of Goldsmiths and reconstituted Gemmological Association of Sou th Africa in 1931 as the Gemmological Association. Its and the Singapore Gemologist Society. name was extended to Gemmological TheJoumal ofGemmology was first Association of Great Britain in 1938, and pu blished by the Association in 1947. I t is a finally in 1944 it was incorporated in that name quarterly, published in January, April, July, under the Companies Acts as a company and October each year, and is issued free to limited by guarantee (registered in England, Fellows and Members of the Association. no. 433063). Opinions expressed by authors are not Affiliated Associations are the necessarily endorsed by the Association. Gemmological Associa tion of Australia, the

Notes for Contributors The Editors are glad to consider original is consistent with dear indication of the articles shedding new light on subjects of content of the paper. I t should be followed by gemmological interest for pu blication in the the names (with initials) of the authors and by Journal. Articles are not normally accepted their addresses. A short abstract of 5 0-1 00 which have already been published elsewhere words should be provided. Papers may be of in English, and an article is accepted only on any length, but long papers of more than the understanding that (1) full information as 10 000 words (unless capable of division into to any previous publication (whether in parts or of exceptional importance) are English or another language) has been given, unlikely to be acceptable, whereas a short (2) it is not under consideration for publica tion paper of 400-500 words may achieve early elsewhere and (3) it will not be published publication. elsewhere without the consent of the Editors. Twenty five copies of individual papers are Papers should be su bmitted in duplica te on provided on request free of charge; additional A4 paper. They should be typed with double copies may be supplied, bu t they must be line spacing with ample margins of at least ordered at first proof stage or earlier. 25mm all round. The title should be as brief as Volume 21 No. 6. April 1989

1 hcJournal of Gemmology

Contents

Notes from the Laboratory - 14 K. Scarratt 339

Proceedings of the First International Amber Symposium H. Fraquet 347

The Dresden Green G. Bosshart 351

Aqua Aura' enhanced quartz specimens R.C. Kammerling and J J. Koivula 364 Methods for the distinction of natural and synthetic citrine and prasiolite K> Schmelzer 368

Proceedings of the Gemmological Association of Great Britain and Association Notices 392

Letters to the Editor 394

Copyright© 1989 Gemmological Association of Great Britain Registered Office: Saint Dunstan's House, Carey Lane, London EC2V 8AB

ISSN: 022-1252

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