Volume 23 No. 8. October 1993 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 Lawrence Bragg, CH, OBE, MC, B.Sc, FRS Sir Frank Claringbull, Ph.D., F.Inst.P., FGS Vice-Presidents : R. K. Mitchell, FGA A.E. Farn, FGA D.G. Kent, FGA E. M. Bruton, FGA, DGA Council of Management CR. Cavey, FGA TJ. Davidson, FGA N.W. Deeks, FGA, DGA I. Thomson, FGA V.P. Watson, FGA, DGA R.R. Harding, B.Sc., D.Phil., FGA, C. Geol. Members' Council A. J. Allnutt, M.Sc, G.H. Jones, B.Sc, Ph.D., P. G. Read, C.Eng., Ph.D., FGA FGA MIEE, MIERE, FGA, DGA P. J. E. Daly, B.Sc, FGA J. Kessler I. Roberts, FGA P. Dwyer-Hickey, FGA, G. Monnickendam R. Shepherd DGA L. Music R. Velden R. Fuller, FGA, DGA J.B. Nelson, Ph.D., FGS, D. Warren B. Jackson, FGA F. Inst. P., C.Phys., FGA CH. Winter, FGA, DGA Branch Chairmen: Midlands Branch: D.M. Larcher, FBHI, FGA, DGA North-West Branch: I. Knight, FGA, DGA Examiners: A. J. Allnutt, M.Sc, Ph.D., FGA G. H. Jones, B.Sc, Ph.D., FGA L. Bartlett, B.Sc, M.Phil., FGA, DGA D. G. Kent, FGA E. M. Bruton, FGA, DGA R. D. Ross, B.Sc, FGA C R. Cavey, FGA P. Sadler, B.Sc, FGS, FGA, DGA S. Coelho, B.Sc, FGA, DGA E. Stern, FGA, DGA A.T. Collins, B.Sc, Ph.D Prof. I.Sunagawa, D.Sc. B. Jackson, FGA C Woodward, B.Sc, FGA, DGA E. A. Jobbins, B.Sc, C Eng., FIMM, FGA Editor: E. A. Jobbins, B.Sc, C.Eng., FIMM, FGA Editorial Assistant: Mary A. Burland The Gemmological Association and Gem Testing Laboratory of Great Britain 27 Greville Street, London EC1N 8SU Telephone: 071-404 3334 Fax: 071-404 8843 TheJournal of Gemmology VOLUME 23 NUMBER EIGHT OCTOBER 1993 Cover Picture Brooch set with pink Argyle diamonds, maximum width approx 7cm; 1068 pink diamonds and 160 white diamonds weighing a total of 16.31 ct and 3.45 ct respectively. See 'Gemmological properties of Type la diamonds with an unusually high hydrogen content' pp.451-60. Photo courtesy of Graff, 6-7 New Bond Street, London Wl. ISSN: 0022-1252 © Copyright the Gemmological Association ISSN: 0022-1252 J. Gemm, 1993,23,8 450 STUDENT STARTER SET AN IDEAL STARTER SET FOR ALL STUDENTS OF GEMMOLOGY THIS SET INCLUDES: 18mm 1 Ox Loupe (ovailable in chrome or matt black finish) Medium Stone Tongs Chelsea Colour Filter OPL Spectroscope SPECIAL INTRODUCTORY PRICE £60.00 plus VAT, postage and packing Normal Retail Price £66.95 plus VAT, postage and packing GAGTL members receive an additional 10% discount on the Special IntroducTory Price To order your set please use the order form following p.496 (Please quote your membership number when placing an order) Gemmological Instruments Limited • FIRST FLOOR, 27 GREVILLE STREET, (SAFFRON HILL ENTRANCE), LONDON EC1N 8SU • Tel: 071 404 3334 Fax: 071 404 8843 J. Gemm., 1993, 23, 8 451 Gemmological properties of Type Ia diamonds with an unusually high hydrogen content Emmanuel Fritsch* and Ken Scarratt† *GIA Research, Santa Monica, CA, USA †GIA Gem Trade Laboratory, New York, NY, USA Abstract erties of natural and treated coloured diamonds, One hundred and thirty-nine Type Ia diamonds that we have studied a number of diamonds with showed unusually intense hydrogen-related absorptions unusual characteristics. For example, we recently in the infrared range were studied; they are referred to as reported on a greyish-blue coloration in diamond 'H-rich diamonds' for brevity. We demonstrate that the believed to be caused by hydrogen-related colour various kinds of H-rich diamonds often have a number centres (Fritsch and Scarratt, 1992). The presence of gemmological and physical properties in common, for example a yellow luminescence, certains types of colour of hydrogen in diamond can be detected by a series of sharp absorptions in the infrared region, zoning and clouds of sub-microscopic inclusions. We 1 also report the discovery of several new hydrogen-related especially at 1405 and 3107 cm , which have been absorptions in the infrared and the visible ranges, some known since 1961 and attributed by Charette to giving rise to a violet colour never described before in C-H bonds (Charette, 1961). These two frequen­ coloured diamonds. cies are also known as hcob (1405 cm1), the Key words: Diamond, Hydrogen, Infrared, Colour elementary frequency for the bending motion of centre. the C-H bond, and hcos (3107 cm1) the elemen­ tary frequency for the stretching motion of the Introduction C-H bond. In recent years hydrogen has been recognized as Over the last five years, a number of gem-quality a common impurity in natural Type Ia diamonds diamonds exhibiting strong C-H bands at 3107 (Woods and Collins, 1983), in addition to the cm-1 have become available. For convenience, well-known nitrogen (and possibly boron) impu­ these diamonds are hereafter called 'H-rich dia­ rities. Little is known, however, of the influence monds' but, strictly speaking, they only are that this hydrogen impurity may have on the diamonds with unusually intense hydrogen- optical properties of such diamonds, in particular related infrared absorptions. These diamonds, their colour. In the course of the coloured although they may have different appearances, diamond project, undertaken at GIA Research present a number of gemmological properties in since 1986 in order to better understand the prop- common. The large number of samples we Fig. 1. Four typical H-rich diamonds, ranging in colour from Fig. 2. Greyish-violet 0.88 ct pear-shaped diamond and brown- greyish-yellow (0.28 ct, left), to light brownish-yellow (1.02 yellow 1.20 ct round brilliant-cut, both from the Argyle mine ct, centre) to light grey (0.09 and 0.15 ct, right). Stones in western Australia. They represent typical examples of H- courtesy Davenport Jewelry Company, Dallas, Texas. Photo rich diamonds described in detail in this paper. Stones by Robert Weldon courtesy of Argyle Diamonds. Photo by Robert Weldon © Copyright the Gemmological Association ISSN: 0022-1252 452 J. Gemm., 1993, 23, 8 Fig. 3. The vast majority of 'white' or 'opalescent' diamonds, such as Fig. 5. Brownish colour zones limited by planar borders in a greyish- these three round brilliant-cuts from the Panna mine in India green chameleon diamond. Magnification lOx. ranging from 0.30 to 0.33 ct, are also H-rich diamonds. Photomicrograph J.I. Koivula Stones courtesy Malhotra Inc., New York. Photo by R. Weldon studied (over one hundred) has enabled us to doc­ a Nicolet 60SX FTIR spectrometer at a resolution ument a number of absorptions in the infrared and of 4 cm1 in the range 400-25000 cm1. Use of a visible ranges related to the presence of the hydro­ microbeam chamber allowed for maximum energy gen impurity, some of which had never been output. described before. In particular, some rare hydro­ All samples were selected because they exhibit gen-rich diamonds from Argyle in western an absorption band at 3107 cm1 that is particu­ Australia exhibit a violetish-grey to greyish-violet larly intense, generally comparable or superior in colour never described before in coloured dia­ intensity to the intrinsic two-phonon diamond monds. absorption around 2450 cm1 (Figure 4. We indi­ cate on this figure a position of 3105 cm1, not Materials and methods 3107, because our spectra are done at a resolution The 139 samples examined in this study were of 4 cm'1 only). all faceted gem-quality diamonds, on loan from For this report, we have tentatively distin­ private parties. They represent a wide range of guished four types of H-rich diamonds on the colour with essentially yellow, grey (Figure 1) or basis of their properties: the 'brown to greyish- brown as the main component (for 78 of them), yellow family' (66 samples), the £grey to violet but also bluish-grey to greyish-violet (for 6 of family' (14), white diamonds (8) and finally them), white (also called 'opalescent diamonds' in 'chameleon diamonds' (36). 15 samples could not the trade; 8 samples) and blue and green (47 be classified because the necessary data were not samples). Their geographical origin is generally available for various reasons. We call 'chameleon unknown, as is unfortunately the case with most diamonds' those that typically change reversibly diamonds. However, the bluish-grey to greyish- from a grey-green to a brighter yellow colour when violet stones are all from Argyle, as well as one heated in the flame of an alcohol lamp. Such pho- brown-yellow (Figure 2) and one greenish-yellow tochromic behaviour was formerly described by stone. A series of three white diamonds is from the Raal and Robinson (1982) in treated Type Ia dia­ Panna mine, India (Figure 3). monds and in some natural green diamonds from This sampling includes 31 stones either known the South African gold mines (Raal, 1969). Brief to be treated, or established to be so based on cri­ gemmological reports on chameleon diamond teria explained elsewhere (Fritsch and Shigley, behaviour can be found in Crowningshield (1975) 1989 and 1991). Although most of these treated, and Fryer (1981, 1982). hydrogen-rich stones were essentially green or blue (sample 8; Fritsch and Shigley, 1989), we Gemmological properties documented also' some that were essentially yellow Microscopic, examination (sample 2; ibid.). Sixty-four of the 131 H-rich diamonds that are All data collection was done at GIA Research.