Volume 24 No. 3. July 1994 The Journal of Gemmology The Gemmological Association and Gem Testing Laboratory of Great Britain President E.M. Bruton Vice-Presidents A.E. Farn, D.G. Kent, R.K. Mitchell Honorary Fellows R.T. Liddicoat Jnr., E. Miles, K. Nassau, E.A. Thomson Honorary Life Members DJ. Callaghan, E.A. Jobbins Council of Management CR. Cavey, TJ. Davidson, N.W. Deeks, E.C. Emms, R.R. Harding, I. Thomson, V.P. Watson Members' Council A.J. Allnutt, P.J.E. Daly, P. Dwyer-Hickey, R. Fuller, B. Jackson, J. Kessler, G. Monnickendam, L. Music, J.B. Nelson, K. Penton, P.G. Read, I. Roberts, R. Shepherd, R. Velden, C.H. Winter Branch Chairmen Midlands: J.W. Porter North West: L Knight Examiners A.J. Allnutt, M.Sc, Ph.D., FGA L. Bartlett, B.Sc, M.PhiL, FGA, DGA E.M. Bruton, FGA, DGA CR. Cavey, FGA S. Coelho, B.Sc, FGA, DGA AT. Collins, B.Sc, Ph.D. B. Jackson, FGA, E.A. Jobbins, B.Sc, CEng., FIMM, FGA G.H. Jones, B.Sc, Ph.D., FGA D.G. Kent, FGA R.D. Ross, B.Sc, FGA P. Sadler, B.Sc, FGS, FGA, DGA E. Stern, FGA, DGA Prof. I. Sunagawa, D.Sc M. Tilley, GG, FGA C Woodward, B.Sc, FGA, DGA The Gemmological Association and Gem Testing Laboratory of Great Britain 27 Greville Street, London EC1N 8SU Telephone: 071-404 3334 Fax: 071-404 8843 The Tourna• ^LJr mrMmJÊL Mm m*^/WLJÊLl o ^rf JL. Gemmology VOLUME 24 NUMBER THREE JULY 1994 Editor Dr RR. Harding Production Editor MA. Burland Assistant Editors M.J. O'Donoghue P.G. Read Associate Editors S.M.Anderson London Dr C.E.S. Arps Leiden G. Bosshart Zurich Dr A.T. Collins London Dr J.W. Harris Glasgow Prof. R.A. Howie Derbyshire DrJ.M. Ogden Cambridge Dr J.E. Shigley !Sant a Monica Dr D.C.Smith Paris E. Stern London Prof. I. Sunagawa Tokyo Dr M. Superchi Milan CM. Woodward London Any opinions expressed in The Journal ofGemmology are understood to be the views of the contributors and not necessarily of the publishers. Cover Picture Carved citrine lion face set in an 18ct gold and diamond brooch by Stephen Webster. Photograph by Bob J. Maurer, FGA, DGA (See 'Photographic Competition' p.216) ISSN: 0022-1252 138 J. Gemm., 1994, 24, 3 Editorial Following the announcements in the to identify gems you should have access to April issue of the Journal the new editorial the most up-to-date comparative informa­ structure is now in place and I am very tion. But there is so much information pleased to have the support of Michael available that it can be difficult to find O'Donoghue and Peter Read as Assistant what is relevant to a particular problem in Editors. They will oversee book reviews a reasonable length of time. Nevertheless, and abstracts respectively. For assessing we hope to assist readers in this process new manuscripts submitted for publication with an increased coverage of abstracts. To we are at once honoured and pleased to this end permission has been obtained welcome a distinguished group of from colleagues in related fields to reprint Associate Editors. They hail from many abstracts not normally seen by many of our parts of the world and cover a wide range members. Further, the abstracts will be of gem, diamond, pearl and trade exper­ arranged in the following categories: dia­ tise, some of which has already been put to monds, gems, instruments, jewellery and good use in appraising the contributions in synthetics. this issue. The most noteworthy change of all in this The opening paper deals with the ques­ issue, however, is the appearance on the tion of origins of gems and with the factors inside front cover of Eric Bruton's name as important in assessing how reliable origin President. For over three years since the information might be. The precise descrip­ death of Sir Frank ClaringbuU the GAGTL tion of features in gems is paramount if has been without a President and we are there is to be clear communication, and this delighted that, on the invitation of the applies as much to origins as to the Council of Management, Eric Bruton descriptions of new synthetic sapphires, agreed to become our next President and moonstones, vesuvianite and the pink sap­ was elected at the Annual General Meeting phires covered in the other contributions. on 13 June. A man of many talents, his A prospect of life in the wild is provided gemmological contributions include the by a paper on how to pan for gem minerals standard textbook on diamonds and it is and, when you bring your concentrates partly in recognition of this that the back to base, just apply specific gravity GAGTL Conference in October incorpo­ techniques explained by Dr Farrimond to rates a major diamond theme under the help distinguish the gems. title 'Diamonds and modern gem develop­ It is a long-recognized fact that in order ments'. R.R.H. J. Gemm., 1994,24, 3 139 Origin determination for gemstones: possibilities, restrictions and reliability Dr H A. Hanni, FGA SSEFSwiss Gemmological Institute, Zurich, Switzerland decomposition of the parent rock. Abstract In the trade the terms Burma, Pailin and The gemmological 'origin' means the Kashmir have been applied to what are geographical locality of a gemstone perceived as the most desirable gems to deposit. Origin names should neither be own but since they have a geographical used as a description of a colour type meaning, they should not be used to nor to express a certain quality. For the express a particular colour of gemstone. It determination of origin in a gemmologi­ is common knowledge that one deposit cal laboratory different chemical and produces a range of colours, some of physical properties are considered, e.g. which may be found in other deposits, too. inclusions, colour zoning, chemical com­ The need in the gem trade for certifica­ position and spectral characteristics. tion of origin seems restricted to a few Therefore, sophisticated equipment is varieties of gemstones only and to a small essential and instrumentation such as number of deposits with a high reputation. spectrophotometers (UV-VIS-IR), For many people the origin 'Burma' may EDXRF, SEM and optical microscopy be commercially meaningful, whereas should be applied. Some of the deter­ 'Malawi' as an origin for a ruby does not mined properties may be diagnostic for create an increased interest. Itshould again a definite source of gemstones. For a be stressed that a certain origin does not reliable interpretation a large collection necessarily mean that all crystals from that of comparison samples of known origin source are of high quality. and reference da ta are necessary. Some gemstones can indicate their place Furthermore, the knowledge has to be of origin through their physical and chemi­ updated repeatedly by adding new cal properties, and by their inclusions and information through research, the latest growth structures if these are clearly dis­ literature and by exchange of experi­ tinguishable from all other types. Thus, ence. Where data released from a stone these properties must be unique by them­ are insufficient or ambiguous an selves or in combination. The greater the opinion of origin should not be given. number of individual and characteristic properties found in a certain stone, the more reliable is a determination of origin. Introduction Valuable characteristics should not only A definition of the term 'origin' as used positively testify a certain origin but at the in gemmology should logically be the same time exclude other possibilities. starting point of this paper. 'Origin' should Consequently in determining the origin indicate the geographical origin of a gem­ of a gemstone the expert must be aware stone. This is either in the primary deposit not only of the properties of similar stones in the parent rock or in a secondary from the locality in question, but of the deposit resulting from transport and accu­ whole set of properties of similar stones mulation of gemstones after from all other localities (Figure 1). Only the © Copyright the Cemmological Association ISSN; 0022-1252 140 J. Gemm., 1994,24, 3 Fig. 1. A large collection of reference material is an important tool for recording and comparison of gemstone characteristics. It is indispensable for laboratories doing origin determination. exclusive features, unique for a particular • transport process and transport deposit, are called diagnostic properties! medium involved for gemstone con­ Depending on the complexity of the forma­ stituents tion of the gemstone crystals, the • type of energy source for the forma­ geological environment, the type and tion (intruding pegmatite, number of characteristics can be quite metamorphosis) varied. • partial pressure of free oxygen, redox situation Gemstone formation • cooling rate and behaviour of pres­ The formation of a gemstone crystal sure (static or oscillating) during or requires a number of more or less impor­ after formation tant conditions. Some of the main • deformation history of parent rock conditions, causing general or individual and crystal during its period of properties of gemstones are the following: growth All these factors affect the individual char­ Basic conditions pertaining to gemstone crystal acteristics of a gemstone crystal, and result formation in differences regarding the following: • availability of main constituent chemi­ cal elements, speed of growth Features which may impart individual charac­ • type and concentration of available teristics to gemstones trace elements, variation in their con­ • size and shape of crystals, growth centration and relative ratio zoning J. Gemm., 1994, 24, 3 141 • twinning tation of the results. A collection of com­ • colour, colour homogeneity, colour parison stones (from all deposits, showing variation the variability within a population) for ref­ • trace element mixture ( including erence, files containing the analytical 'invisible' trace elements) results measured over the years and a • solid inclusions (e.g.