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Volume 25 / No. 4 / 1996 he Journa TGemmolog The Gemmological Association and Gem Testing Laboratory of Great Britain President E.M. Bruton Vice-Presidents AE. Farn, D.G. Kent, RK. Mitchell Honorary Fellows R.T. Liddicoat [nr., E. Miles, K. Nassau Honorary Life Members D.}. Callaghan, E.A Iobbins, H. Tillander Council of Management CR Cavey, T.}. Davidson, N.W. Deeks, RR Harding, 1.Thomson, v.P. Watson Members' Council AJ. Allnutt, P. Dwyer-Hickey, R. Fuller, B. Jackson, J. Kessler, G. Monnickendam, L. Music, J.B. Nelson, K. Penton, P.G. Read, 1. Roberts, R Shepherd, CH. Winter Branch Chairmen Midlands: J.W. Porter North West: 1. Knight Scottish: J. Thomson Examiners AJ. Allnutt, M.Sc., Ph.D., FGS S.M. Anderson, B.SdHonst 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. AG. Good, FGA, DGA CJ.E. Hall, B.Sc.(Hons), FGA G.M. Howe, FGA, DGA G.H. Jones, B.5c., Ph.D., FGA H.L. Plumb, B.Sc., FGA, DGA RD. Ross, B.Sc., FGA DGA P.A. Sadler, B.Sc., FGA, DGA E. Stem, FGA, DGA Prof. 1. Sunagawa, D.Sc. M. Tilley, GG, FGA CM. Woodward, B.5c., FGA DGA The Gemmological Association and Gem Testing Laboratory of Great Britain 27 Greville Street, London EC1N 8SU Telephone: 0171-404 3334 Fax: 0171-404 8843 f% The Journal of | Gemmology VOLUME 25 NUMBER 4 OCTOBER 1996 Editor Dr R.R. Harding Production Editor M.A. Burland Assistant Editors M.J. O'Donoghue P.G. Read Associate Editors S.M. Anderson London Dr C.E.S. Arps Leiden G. Bosshart Lucerne Prof. A.T. Collins London Dr J.W. Harris Glasgow Prof. RA. Howie Derbyshire DrJJVLOgden Cambridge DrJ.E.Shigley Santa Monica Prof. 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 # *\ Fine gem quality rubellite crystal, 75 mm long, from the Cruzeiro mine, Minas Gérais, Brazil. See 'The location, geology and mineralogy of gem tourmalines in Brazil' on pp. 263-98 ISSN: 1355-4565 262 J. Gemm, 1996, 25, 4 New President Professor Howie receiving his Badge of Office from Vivian Watson, Chairman at the AGM. At the Annual General Meeting of the Countless students and professional geol­ Gemmological Association and Gem ogists have perhaps most appreciated Testing Laboratory held on 10 June,* his involvement with W.A. Deer and Eric Bruton stepped down from his two- J. Zussman in producing Rock-Forming year term as President and handed over Minerals and a condensed version An his badge of office to the incoming introduction to rock forming minerals. This President, Professor R.A. Howie. work was published in five volumes in Bob Howie graduated in Natural Sciences 1962 and with the later edition has been an at Cambridge university and followed this integral part of the tremendous growth of with a doctorate on Indian metamorphic activity in the earth sciences in the last rocks, graduating in 1952. After a period at three decades. Manchester University, he moved to King's A lifelong interest in gemstones has found College, London, and was appointed to a expression in lectures to a wide range of personal chair in mineralogy in 1972. He audiences and his presidency will reinforce was President of the mineralogical Society the strong links that the Gemmological in 1978-80 and since 1966 has edited Association and the Laboratory have Mineralogical Abstracts, being responsible always had with King's College. for a prodigious output of information in a digestible and relevant form appreciated * A report of the Annual General Meeting and the throughout the world. President's address are published on pp 312-14. J. Gemm., 1996,25,4,263-298 263 The location, geology and mineralogy of gem tourmalines in Brazil Jacques P. Cassedanne, Dr. Sc. *, and Maurice Roditi, FGA ** * Institute of Geosciences UFRJ, Cidade Universitaria, 21.910.240, Rio de Janeiro ** Roditi Jewellers, Rua Visconde de Piraja, 482, 22.410.002, Rio de Janeiro Abstract contain. The tourmaline-bearing peg­ A comprehensive survey of matites mainly consist of K-feldspar Brazilian gem tourmalines, mainly variably perthitized, albite, muscovite green, blue, pink and red elbaite, and milky quartz with some lepidolite, including their gemmological proper­ schorl and locally huge tabular crystals ties and significant inclusions is given. of spodumene. Accessory minerals are The tourmalines are recovered from listed for different localities. granitic pegmatites and detrital The main area producing tourma­ deposits. Tourmaline-bearing peg­ line is the 'Eastern pegmatitic province' matites, which commonly are lens­ of Minas Gerais. One general and three shaped, are variable in their strike and detailed maps of specific areas show dip, and show a range of patterns of the location of the tourmaline deposits, zoning and albitization. Wallrocks are and their regional zonation and age are mica schists, quartzites or rarely granite briefly examined. Short descriptions or gneiss, all Precambrian in age. The are given for the most important peg­ pegmatites occur either singly or in matites, and methods of prospecting fields or clusters and belong to the and working, generally by hand, are Brazilian tectonic cycle (650-450 m.y.). discussed. Five types of gem-bearing pegmatites Weathering of tourmaline-bearing are described: pegmatites produces detrital deposits, • poorly differentiated, almost homo­ eluvial and alluvial. Only eluvial geneous, with small albitic replace­ deposits sometimes yield deposits of ment bodies; economic worth and they also are • poorly differentiated with strong worked by hand. albitization; Non-pegmatitic deposits of tour­ • zoned with small albitic replacement maline include the Brumado mine bodies; (Bahia) which produces fine red uvite • zoned with strong albitization; crystals and the Serra Branca prospect • lithium-rich, very well zoned, with (Paraiba) which produces large black strong albitization. dravite specimens. Gem tour,malines occur in the inner parts of the pegmatites, on each side of a quartz core or concentrated in Keywords: Tourmaline, pegmatite, eluvial pockets, which are variable in shape deposits, gem mining, Brazil and size, as are the crystals that they © Gemmological Association and Gem Testing Laboratory of Great Britain ISSN: 1355-4565 264 J. Gemm., 1996, 25, 4 Introduction trading. In this paper the mineralogical Tourmaline is one of the most remarkable species will not be specified but, in com­ coloured gemstones mined in Brazil where, mon with daily use, the tourmaline will be erroneously, for a long time it was mar­ described by means of its colour. keted as Brazilian emerald, peridot, sap­ Tourmaline is trigonal hemimorphic and phire and chrysolite. Hardness, relatively Brazilian elbaite (rubellite) was used by Ito high specific gravity and chemical resis­ and Sadanaga in order to determine its tance explain the abundance of its occur­ structure in 1951. Tourmaline commonly rence: tourmaline is found mainly in meta- occurs as long, vertically striated prisms, morphic rocks, quartz veins and granite with some crystals reaching up to one pegmatites which produce the bulk of the metre in length. Crystals show a rounded gems. Therefore the deposits are many and triangular cross-section with 3, 6 or 9 main have been the subject of a range of publica­ faces, and flat or complex terminations tions from old compilations to recent travel with pyramids of 3, 6 or more faces, com­ records (e.g. Ferraz, 1929; Calmbach, 1938; monly irregularly developed or asymmet­ Putzer, 1956; Proctor, 1985a, 1985b). rical. Short crystals, thin tablets, needles, However, geological reports on the radiating parallel, stacked and irregular deposits are rare and as a result, our pur­ crystal groups are common as are compact pose is to summarize the main geological or felty (asbestiform) masses (Coelho, and mineralogical features of the tourma­ 1948) (Figure 1) identical to those reported line deposits, both primary and secondary, from California (Jahns and Wright, 1951). and to examine the gems produced. Tourmaline pebbles and gravels are com­ Tourmaline has no industrial application mon. Twins are rare, but some are reported and is mined only to recover crystals by Madelung (1883) and Frondel (1948). suitable for cutting and use in jewellery, Crystallographic reviews of tourmaline or for other ornamental purposes, or forms were published by Reimann (1907) less commonly for collectors. Tourmaline and Goldschmidt (1923). is the name given to a group of borosili- The streak is colourless and lustre is vit­ cates of general formula: reous to waxy. Crystals are transparent, WX3Y6(B03)3Si6018(0,OH,F) where translucent or opaque. Elbaite is pink or W = Ca, K, Na; X = AI, Fe2+, Fe3+, Li, Mg, green, also colourless, red, orange, yellow, Mn2+; Y = Al, Cr3+, Fe3+, V3+ (Fleischer and blue, purple, white or black (which is Mandarino, 1995). The most sought after smoky purple when strongly illuminated - varieties, green and blue (indicolite) or pink Prescott and Nassau, 1978). Elbaite from and red (rubellite), are traditionally referred Parafba displays outstanding blue, purple, to as elbaite Na(Al,Li)3Al6(BQ3)3Si6018(OH)4; green and light purple colours. The colour and the brown varieties are referred to as is either homogeneous or shows variations dravite NaMg3Al6(B03)3Si6018(OH)4 or uvite within the crystal. Multicoloured tourma­ 2+ (Ca,Na)(Mg,Fe )3Al5Mg(B03)3Si6018(OH,F)4. lines exhibit either one or more fairly regu­ Tourmaline is the gem with the widest lar patterns of colour zoning or irregular, array of colours. This is due to the many patchy arrangements of their diverse hues. isomorphic substitutions that occur and Regular patterns of zoning may be either explains why only the colour is taken into perpendicular to the c-axis (roughly paral­ account during transactions by miners, lel to the pedion face) or parallel to c lapidaries and jewellers.
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