Volume 22 No. 5. January 1991 The Journal of Gemmology THE GEMMOLOGICAL ASSOCIATION AND GEM TESTING LABORATORY OF GREAT BRITAIN OFFICERS AND COUNCIL Past Presidents: Sir Henry Miers, Ma, D.Sc, FRS Sir William Bragg, OM, KBE, FRS Dr. G.F Herbert Smith, CBE, MA, D.Sc. Sir Frank Claringbull, Ph.D., F.Inst.E, FGS Vice-President: R. K. Mitchell, FGA Council of Management D.J. Callaghan, FGA N.WDeeks,FGA N.B. Israel, FGA E.A. Jobbins, B.Sc, C.Eng., FIMM, FGA I. Thomson, FGA V.E Watson, FGA K. Scarratt, FGA : Chief Executive R.R. Harding, B.Sc, D.Phil., FGA : Director of Gemmology Members' Council A.J.Allnutt,M.Sc, D. Inkersole, FGA PG. Read, C.Eng., Ph.D.,FGA B. Jackson, FGA MIEE, MIERE, FGA C. R. Cavey, FGA G.H. Jones, B.Sc, Ph.D., FGA I. Roberts, FGA P J. E.Daly, B.Sc, FGA H. Levy, M.Sc,BA, FGA E.A. Thomson, T. Davidson, FGA J. Kessler Hon. FGA R. Fuller, FGA G. Monnickendam R. Velden J.A.W Hodgkinson, L. Music D. Warren FGA J.B.Nelson, Ph. D., FRMS, C.H. Winter, FGA F.Inst.E, FGA Branch Chairmen: Midlands Branch: D.M. Larcher, FBHI, FGA North-West Branch: W Franks, FGA Examiners: A. J. Allnutt, M.Sc, Ph.D., FGA D. G. Kent, FGA E. M. Bruton, FGA P Sadler, B.Sc, FGS, FGA C. R. Cavey, FGA K. Scarratt, FGA A. E. Farn,FGA E. Stern, FGA R. R. Harding, B.Sc, D.Phil., FGA M. Virkkunen, M.Phil., FGA E. A. Jobbins, B.Sc, C. Eng., FIMM, FGA C. Woodward, B.Sc, FGA G. H. Jones, B.Sc, Ph.D., FGA Editor: E. A. Jobbins, B.Sc, C.Eng., FIMM, FGA Editorial Assistant: Mary A. Burland Curator: C. R. Cavey, FGA The Gemmological Association and Gem Testing Laboratory of Great Britain 27 Greville Street, London EC1N 8SU Telephone: 071-404 3334 Fax: 071-404 8843 ^Journal of Gemmology VOLUME 22 NUMBER FIVE JANUARY 1991 Cover Picture Two small secondary synthetic spinel 'satellites'grow from an octahedral face on the main crystal. Magnified 5x. (See 'Gemmological investigation of a synthetic spinel crystal from the Soviet Union'by J.I. Koivula, R.C. Kammerling and E. Fritsch,p.300). Photomicrograph by John I. Koivula. ISSN: 0022-1252 258 J. Gemm., 1991, 22, EXAMINATIONS IN GEMMOLOGY1991 Refresher Courses The courses outlined below aim particularly to help gemmology students who will be sitting their Diploma Examinations, but one course also caters for the Preliminary Examinations. The tutorials, which may extend over one, two or three days (as set out below), usually include mock practical examinations. Some courses provide tuition only, whereas others include meals and accommodation. NATURAL HISTORY MUSEUM (formerly Geological Museum), South Kensington, London. 6-7 April, 13-14 April, 20-21 April Tutors: Various GA/GTL lecturers Details: 071-404 3334 GENESIS Epsom, Surrey 9-10 May, 30-31 May, 6-7 June, 13-14 June Tutors: Colin Winter, Hilary Taylor Details: 03727 42974 or 071-404 3334 HATTON GARDEN AREA London 11 June (Preliminary), 12-13 June (Diploma) Tutors: Michael O'Donoghue, Peter Read Details: R. Huddlestone, 071-404 5004 NELSON GEMMOLOGICAL INSTRUMENTS Sundays around Easter (provisional) Tutorials at various venues depending upon demand. Topics include four difficult Cs - crystallography, chemistry, colour and cut. Tutor: Jamie Nelson Details: 071-435 2282 or 071-435 0331 WEST DEAN COLLEGE near Chichester, West Sussex 7-9 June (also 2-5 November) Tutor: Peter Read Details: Sue Overman, 0243 63301 UPTON HALL Upton, Newark, Notts. 4-5 March, 6-8 March, 4-5 June, 6-7 June (also 23-24 September, 25-27 September). Course contents vary - please check. Meals and accommodation included. Tutors: Alan Hodgkinson, Pat Daly Details: Carol Moore, 071-387 6611 Examination Dates The examination dates for 1991 are as follows: GEM DIAMOND EXAMINATION: Monday 3 June EXAMINATIONS IN GEMMOLOGY: Preliminary - Tuesday 25 June Diploma Theory - Wednesday 26 June Diploma Practical - Thursday 27 June The final date for receiving examination entry forms is 31 March. J.J. Gemm.,Gemm., 1991,22,51991, 22, 5 252599 ColourColour asas a guideguide toto thethe compositioncomposition ofof scapolitescapolite fromfrom BurmBurmaa A.G. Couper A.G. Couper Department of Mineralogy, British Museum (Natural History), London* Department of Mineralogy, British Museum (Natural History), London* TheThe PainPain collectioncollection ofof gemstonesgemstones (BM(BM 19731973,, valuevaluess andand greygrey andand colourlesscolourless specimensspecimens thethe 246-375)246-375) frofromm MogokMogok,, BurmaBurma,, bequeathebequeathedd toto thethe highest.highest. IInn betweebetweenn werweree groupsgroups ofof mauvemauve,, pink,pink, BritishBritish MuseumMuseum (Natural(Natural History)History) inin 1973,1973, isis yellow,yellow, greenish-yellowgreenish-yellow andand beigbeigee stonesstones inin orderorder ooff remarkableremarkable notnot onlyonly foforr ththee numbenumberr ofof gem-qualitygem-quality increasingincreasing refractivrefractivee indexindex andand specificspecific gravity.gravity. mineralmineral speciesspecies foundfound inin suchsuch a relativelrelativelyy smallsmall areaarea ScapoliteScapolite withwith suchsuch a rangerange ofof colourcolour hahass notnot beenbeen ofof Burma,Burma, bubutt alsoalso forfor thethe extraordinaryextraordinary rangerange ooff foundfound atat anyany otherother locality.locality. colourcolour withinwithin somesome ofof thethe speciespeciess oror groups.groups. AAss a generalgeneral rulrulee thethe densitydensity ofof scapolitescapolite increasesincreases ForemosForemostt amongsamongstt ththee latterlatter iiss ththee scapolitscapolitee groupgroup witwithh ththee meionitemeionite contentcontent,, bubutt itit cancan bbee useusedd onlyonly asas whicwhichh hashas marialitemarialite (Na4AI3Si90z4CI)(Na4Al3Si9024Cl) andand meionitemeionite a roughrough guideguide toto composition.composition. PredictionPrediction ofof thethe (Ca4AI6Si60z4C03)(Ca4Al6Si6024C03) asas itsits sodium-richsodium-rich andand calcium­calcium- meionitemeionite percentagpercentagee fromfrom opticaloptical parameterparameterss isis stillstill ricrichh end-membersend-members respectively.respectively. thethe besbestt andand quickestquickest procedure,procedure, accordingaccording toto ThereThere hahass alwaysalways beebeenn muchmuch confusion sur­sur­ UlbricUlbrichh (1973),(1973), andand thethe claimclaim isis mademade thatthat estima­estima­ roundingrounding ththee nomenclaturenomenclature ofof ththee scapolitescapolite groupgroup tiontion fromfrom thethe refractivrefractivee indexindex non0 regressionregression lineline andand inin anan attemptattempt toto simplifysimplify ththee probleproblemm thethe (Ulbrich(Ulbrich 1973,1973, FigureFigure 2 andand equationsequations 5-6,5-6, TableTable 44)) CommissionCommission onon NeNeww MineralsMinerals andand NewNew MineralMineral isis accurateaccurate withinwithin ± 5 perper centcent meionitemeionite atat thethe 9595 perper NameName·ss ofof thethe InternationalInternational MineralogicalMineralogical AssoAsso­­ centcent confidenceconfidence interval.interval. ciationciation hahass approvedapproved thethe followingfollowing proposalsproposals ((P.E TheThe 0.0440.044 differencedifference betweebetweenn thethe higheshighestt andand Bayliss,Bayliss, 1987):1987):-- lowestlowest valuesvalues ofof non0 (the(the refractiverefractive indexindex non0 shouldshould bebe 1.1. TheThe namnamee scapolitescapolite shouldshould bebe retaineretainedd asas a useusedd preferentiallypreferentially overover thethe averageaverage refractivrefractivee indexindex groupgroup namnamee toto encompassencompass mineralsminerals iinn thethe nmnm (Ulbrich(Ulbrich 1973))1973)) indicatesindicates a considerableconsiderable marialite-meionitemarialite-meionite series;series; variancevariance inin compositioncomposition betweenbetween thethe colourlesscolourless andand 2.2. TheThe namesnames ofof marialitemarialite (Na4AhSi90z4CI)(Na4Al3Si9024Cl) andand ththee darkdark blueblue scapolitescapolite fromfrom Burma.Burma. TheThe factfact thatthat meionitemeionite (Ca4AI6Si60z4C03)(Ca4Al6Si6024C03) shouldshould bbee givengiven thethe compositioncomposition ofof scapolitescapolite variesvaries widelywidely waswas speciesspecies status;status; notednoted bbyy DunnDunn et at.,al., (1978)(1978) whenwhen describingdescribing gemgem 3.3. DipyreDipyre andand mizzonitemizzonite shouldshould bbee regardedregarded asas scapolitesscapolites fromfrom world-wideworld-wide localities.localities. AmongAmong thethe varietavarietall names;names; specimensspecimens useusedd forfor thatthat studystudy werweree threthreee fromfrom 4.4. WerneriteWernerite isis synonymoussynonymous witwithh scapolitescapolite andand BurmaBurma andand oneone ofof them,them, G 3674,3674, isis describeddescribed asas shouldshould bbee discarded.discarded. pinpinkk withwith 3030 peperr centcent meionitemeionite contentcontent andand havinhavingg a IntermediateIntermediate membersmembers ofof ththee seriesseries areare givengiven byby refractivrefractivee indexindex non0 = 1.558;1.558; a secondsecond specimen,specimen, R StrunzStrunz (1970)(1970) aass dipyredipyre (MagMez(Ma8Me2 - MaMasMes)5Me5) andand 11157,11157, isis lightlight yellowyellow andand hashas 5757 peperr centcent meionitemeionite mizzonitemizzonite (MasMes(Ma5Me5 - MazMeg).Ma2Me8). Gemmologists,Gemmologists, content;content; thethe thirthirdd specimen,specimen, G 3783,3783, isis colourlesscolourless howeverhowever,, tentendd ttoo ususee onlyonly ththee end-memberend-member names,names, witwithh 7722 perper cencentt meionitemeionite contentcontent andand a refractiverefractive marialitemarialite forfor scapolitesscapolites witwithh Na>CaNa>Ca (in(in atomatom perper index,index,