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Volume 24 No. 2. April 1994 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 A.E. Farn D.G. Kent E. M. Bruton Council of Management C.R. Cavey T.J. Davidson N.W. Deeks E.C. Emms I. Thomson V.P. Watson R.R. Harding Members' Council A. J. Allnutt J. Kessler R. Shepherd P. J. E. Daly G. Monnickendam R. Velden P. Dwyer-Hickey L. Music D. Warren R. Fuller, J.B. Nelson CH. Winter B. Jackson P. G. Read G.H. Jones I. Roberts Branch Chairmen: Midlands Branch: D.M. Larcher, North-West Branch: I. Knight 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 M. Tilley, GGf FGA E. A. Jobbins, B.Sc, C. Eng., FIMM, FGA C. Woodward, B.Sc, FGA, DGA Editor: R.R. Harding Production Editor: Mary A. Burland The Gemmological Association and Gem Testing Laboratory of Great Britain 27 Greville Street, London EC1N 8SU Telephone: 071-404 3334 Fax:071-4048843 TheJournal of Gemmology VOLUME 24 NUMBER TWO APRIL 1994 Cover Picture Three-phase inclusions in quartz consisting of oil, a gas bubble and a small black particle of bitumen. Transmitted light (top) and long-wave ultraviolet light plus low intensity transmitted illumination below. 14x. (See "Fluorescent oil inclusions in quartz' pp. 84-5) Photo by Anthony de Goutière ISSN: 0022-1252 74 J. Gemm, 1994, 24, 2 Alan Jobbins Editor 1986-93 Alan Jobbins resigned from the editorship of The Journal will continue to be a major maga­ the Journal at the end of 1993. The Council of zine for original papers on topics of significance Management has appointed Dr Roger Harding to for gemmologists whether they be in production, succeed him. manufacturing, distribution, testing or research In 1985 Alan became joint Editor of the Journal sectors of the profession. We invite accounts of with J.R.H. Chisholm and took over completely new gemstone research and stimulating reviews in 1986. In that year he launched a new design, of of recent advances for publication. We aim to increased size, which incorporated more colour achieve publication in twelve months or less from illustrations of better quality and enhanced the date of reception of a satisfactory manuscript. already world-wide reputation of the Journal. For many years and throughout his editorship Gemmology is a constantly changing and Alan supplied a constant stream of colour illus­ expanding subject, and we intend that the Journal trations for the Journal - they were superb and should develop to reflect, record and be part of have been a major feature in his articles and lec­ these changes. To this end, an editorial structure tures on gemmology. We hope that Alan will including Assistant and Associate Editors is continue to delight us all with his pictures and planned and will involve a wide range of exper­ with the fruits of his gemmological travels tise. This will enable a thoroughly professional throughout the world. We would also like to assessment of new manuscripts describing the wish him good health and many more years of latest gemmological developments. enjoyment in his gemmological activities. © Copyright the Gemmological Association ISSN: 0022-1252 J. Gemm., 1994, 24, 2 75 Four hessonite occurrences in Orissa, India Dr J. Kanis1 and M. Redmann2 1. Veitsrodt, Germany 2. Idar-Oberstein, Germany Abstract very fine rhodolite, almandine and pyrope- Hessonite garnets from the villages of almandine but also of the hessonite variety of Ghatpara, Dahikbala, Budhido and Burubura in grossular. Orissa, India, are located in the high-grade metamorphic Indian hessonite has been found near Madras khondalite suite and occur either in in the Coimbatore district; in the State of Orissa, calc-silicate lenses or in quartzite-amphibolite near Boirani in the Genjam district and near contact zones. The paragenesis of Orissa's hessonite Daolathgarh in Rajasthan (Rouse, 1986). is linked to regional metamorphic During a United Nations Development processes, probably during Middle Proterozoic Programme (UNDP) exploration mission in times. The colours of the stones are pale yellowish, Orissa (India) recently one of the authors (J.K.) orange to brown and the ranges of the collected light yellowish to brownish hessonite refractive index and density from each locality samples from the Ghatpara deposit, south of the are: Tel river. Later, in November 1992, hessonite Ghatpara: n=1.738-1.752 D=3.56-3.64 g/cm3 samples in yellowish-brown and orange to 3 brownish colours were collected from three other Dahikbala: n=1.750-1.756 D=3.58-3.64 g/cm occurrences near Dahikbala, Budhido and 3 Budhido: n=1.751-1.758 D=3.60-3.63 g/cm Burubura, all in the State of Orissa. Burubura: n=1.759-1.763 D=3.60-3.66 g/cm3 The physical, chemical and microscopic char­ In addition to calcium, aluminium and silicon, acteristics of hessonites from these four different the chemical analyses also show a distinct occurrences are interesting to compare. Grossular content of iron and traces of both manganese and is chemically a calcium aluminium silicate titanium. (Ca3Al2(Si04)3) and forms with andradite and Microscopical study shows that the hessonite uvarovite the ugrandite series (Deer et al, 1982). from Ghatpara is characterized by mineral inclusions, Two kinds of decorative grossular can be distin­ healing cracks with two- or three-phase guished: a transparent and an opaque type. inclusions and growth marks which sometimes Opaque green grossular variety, which is known show strong interference colours under crossed in the trade as 'Transvaal Jade', is a mixture of grossular with vesuvianite. The green colour polarizers. The inclusions in the stones from 3+ Burubura are mainly healing cracks with two- or depends on the chromium (Cr ) content (Bank, three-phase inclusions and growth marks. The 1982). Opaque pink grossular is a mixture of hessonite from Budhido shows a strong oily grossular and hydrogrossular, now know as hib- appearance and mineral inclusions, and the schite where Si04 is partly replaced by (OH)4, and stones from Dahikbala are characterized by the colour is caused by manganese (Bank, 1982). needle-like inclusions, growth marks and some Transparent grossular is known in colourless, mineral inclusions. green, yellowish and orange to brown colours. It is the vanadium (V3+) and/or chromium (Cr3+) Introduction content which is responsible for the green colour, India is an important producer of gemstones and this green grossular is well known under the and rare collectors' specimens, and well known name tsavorite, from East Africa. The yellowish and orange to brownish colour is caused by iron for its abundant gems tone occurrences. There are 3+ many valuable garnet occurrences, not only of (Fe ) and this grossular variety is known as hes- © Copyright the Gemmological Association ISSN: 0022-1252 76 J. Gemm., 1994, 24, 2 Table I. Refractive indices and densities of transparent grossular from previous literature Literature Colour Refractive Density: g/cm3 index Eppler (1984) pure synthetic 1.734 3.594 grossular Bank, H. (1971) colourless 1.732 3.65 Bank, H. and yellowish-green - 1.735-1.759 3.55-3.64 Henn, U. (1988) dark green (contains vanadium) Eppler (1984) light green 1.734-1.738 Eppler (1984) tsavorite (green) 1.739-1.744 3.61 (mostly) Bank, H. et al (1969) yellow 1.745 3.60 Bank, H. et al (1969) brown 1.749 3.73 Webster (1983) hessonite 1.728-1.748 3.65 Eppler (1984) hessonite 1.742-1.748 3.65 (mostly) Manson and hessonite 1.733-1.760 3.59-3.66 Stockton (1982) sonite. The refractive indices and density in the bubbles, halite crystals and a not yet identified transparent varieties vary considerably, depend­ black amorphous substance, which could be ing on the contents of different elements. For bitumen). instance, in the green vanadian grossular the alu­ minium (Al3+) is partly replaced by vanadium Federal State of Orissa (V3+) and chromium (Cr3+). The higher the per­ Geography centage of vanadium (V3+), the more intense is the The State of Orissa is situated on the east coast green colour and the higher are the refractive of India, along the Gulf of Bengal and south-west indices and the density (Bank and Henn, 1988). In of Calcutta. the yellowish to brown grossulars there is a The Mahanadi river flows through the Eastern partial replacement of aluminium (Al3+) by iron Ghats and has a length of 885km. This mighty (Fe3+). Similarly, the refractive indices and the river has been known for the occurrence of allu­ density are higher with increased iron content. vial diamonds for more than 200 years. The hills Strongly corroded apatite and calcite have and mountains of the Eastern Ghats dominate the been found as inclusions in hessonite, as well as morphology of Orissa; the average elevation is diopside and zircon. Typical internal features in about 750m, but a few peaks rise to over 1500m. hessonite are oily-looking streaks, often called 'treacle'.
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  • Refinement of the Crystal Structure of Ushkovite from Nevados De Palermo, República Argentina

    Refinement of the Crystal Structure of Ushkovite from Nevados De Palermo, República Argentina

    929 The Canadian Mineralogist Vol. 40, pp. 929-937 (2002) REFINEMENT OF THE CRYSTAL STRUCTURE OF USHKOVITE FROM NEVADOS DE PALERMO, REPÚBLICA ARGENTINA MIGUEL A. GALLISKI§ AND FRANK C. HAWTHORNE¶ Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada ABSTRACT The crystal structure of ushkovite, triclinic, a 5.3468(4), b 10.592(1), c 7.2251(7) Å, ␣ 108.278(7), ␤ 111.739(7), ␥ 71.626(7)°, V 351.55(6) Å3, Z = 2, space group P¯1, has been refined to an R index of 2.3% for 1781 observed reflections measured with MoK␣ X-radiation. The crystal used to collect the X-ray-diffraction data was subsequently analyzed with an electron microprobe, 2+ 3+ to give the formula (Mg0.97 Mn 0.01) (H2O)4 [(Fe 1.99 Al0.03) (PO4) (OH) (H2O)2]2 (H2O)2, with the (OH) and (H2O) groups assigned from bond-valence analysis of the refined structure. Ushkovite is isostructural with laueite. Chains of corner-sharing 3+ 3+ {Fe O2 (OH)2 (H2O)2} octahedra extend along the c axis and are decorated by (PO4) tetrahedra to form [Fe 2 O4 (PO4)2 (OH)2 3+ (H2O)2] chains. These chains link via sharing between octahedron and tetrahedron corners to form slabs of composition [Fe 2 (PO4)2 (OH)2 (H2O)2] that are linked by {Mg O2 (H2O)4} octahedra. Keywords: ushkovite, crystal-structure refinement, electron-microprobe analysis. SOMMAIRE Nous avons affiné la structure cristaline de l’ushkovite, triclinique, a 5.3468(4), b 10.592(1), c 7.2251(7) Å, ␣ 108.278(7), ␤ 111.739(7), ␥ 71.626(7)°, V 351.55(6) Å3, Z = 2, groupe spatial P¯1, jusqu’à un résidu R de 2.3% en utilisant 1781 réflexions observées mesurées avec rayonnement MoK␣.