The Journal of VolumeGemmolol 26 No. 5 January 1999 y The Gemmological Association and Gem Testing Laboratory of Great Britain Gemmological Association and Gem Testing Laboratory of Great Britain 27 Greville Street, London EClN 8TN Tel: 01714043334 Fax: 0171 4048843 e-mail: [email protected] Website: www.gagtl.ac.uk/ gagtl President: Professor RA Howie Vice-Presidents: E.M. Bruton, AE. Farn, D.G. Kent, RK. Mitchell Honorary Fellows: RA Howie, RT. Liddicoat Jnr, K. Nassau Honorary Life Members: D.J. Callaghan, E.A Jobbins, H. Tillander Council of Management: C.R Cavey, T.J. Davidson, N.W. Deeks, RR Harding, M.J. O'Donoghue, I. Thomson, Y.P. Watson Members' Council: AJ. Allnutt, P. Dwyer-Hickey, S.A Everitt, R Fuller, A.G. Good, J. Greatwood, B. Jackson, J. Kessler, J. Monnickendam, L. Music, J.B. Nelson, P.G. Read, R Shepherd, P.J. Wates, C.H. Winter Branch Chairmen: Midlands - G.M. Green, North West -I. Knight, Scottish - B. Jackson Examiners: AJ. Allnutt, M.5c., Ph.D., FGA, L. Bartlett, B.5c., M.Phil., FGA, DGA, E.M. Bruton, FGA, DGA, C.R Cavey, FGA, S. Coelho, B.5c., FGA, DGA, Prof. AT. Collins, B.5c., Ph.D, AG. Good, FGA, DGA, G.M. Howe, FGA, DGA, G.H. Jones, B.5c., Ph.D., FGA, M. Newton, B.5c., D.Phil., CJ.E. Oldershaw, B.5c. (Hons), FGA, B.L. Plumb, B.5c., FGA, DGA, RD. Ross, B.5c., FGA, DGA, P.A Sadler, B.5c., FGA, DGA, E. Stern, FGA, DGA, S.M. Stocklmayer, B.Sc. (Hons), FGA, Prof. I. Sunagawa, D.5c., M. Tilley, GG, FGA, CM. Woodward, B.5c., FGA, DGA The Journal of Gemmology Editor: Dr RR Barding Assistant Editors: M.J. O'Donoghue, P.G. Read Associate Editors: Dr CE.s. Arps (Leiden), G. Bosshart (Zurich), Prof. AT. Collins (London), Dr J.W. Harris (Glasgow), Prof. RA Howie (Derbyshire), Dr J.M. Ogden (Cambridge), Prof. AB. Rankin (Kingston upon Thames), Dr J.E. Shigley (Carlsbad), Prof. D.C Smith (Paris), E. Stern (London), S.M. Stocklmayer (Perth), Prof. I. Sunagawa (Tokyo), Dr M. Superchi (Milan), CM. Woodward (London) Production Editor: M.A Burland Vol 26, No.5, January 1999 [SSN: 1355-4565 Element mapping of trapiche rubies Dr Karl Schmetzer1, Professor Zhang Beili2, Gao Yan2, Dr Heinz-Jurgen Bernhardt3 and Professor Henry A. Hanni4 1. Marbacher Str. 22b, D-85238 Petershausen, Germany 2. National Gemstone Testing Center, Beijing 100034, RR. China 3. Institutfur Mineralogie, Ruhr-Universitat, D-44780, Bochum, Germany 4. SSEF Swiss Gemmological Institute, CH-4001 Basel, Switzerland ABSTRACT: Chemical zoning in trapiche rubies was examined by X-ray microfluorescence analysis and by electron microprobe analysis. Two- dimensional element maps indicate a chemical variability of Al, Si, Ca, Ti, Cr and Fe within the samples. This chemical variation is mainly due to primary growth zoning as well as due to carbonate and in places silicate inclusions in orientated channels of the host rubies. Secondary iron staining caused by intense weathering of the samples is also observed. Keywords: electron probe, element map, ruby, trapiche, X-ray micro- fluorescence 290Q Introduction In the yellow or white arms of the star and in the boundary zones between the core and rapiche rubies from south-east the six trapezohedral ruby sectors, a massive Asia with a fixed six-rayed star, concentration of tube-like inclusions is Tsimilar in effect to trapiche emeralds observed. These inclusions are orientated from Colombia, were recently described by perpendicular to morphologically dominant Schmetzer et al. (1996a). Information dipyramidal crystal faces; they contain available at present indicates that the liquid, two-phase (liquid/gas) and solid trapiche rubies come from Myanmar and fillings identified as magnesium-bearing Vietnam. They consist of six transparent-to- calcite and dolomite by a combination of translucent ruby sectors separated by the electron microprobe analysis and micro- yellow- or white-appearing arms of a Raman spectroscopy. In black or yellow six-rayed star. In some crystals, the six cores, tube-like structures with identical arms (which, unlike typical asteriated fillings also run parallel to the c-axis, i.e. gems, are fixed - that is, they do not move perpendicular to basal faces of the trapiche when the stone or light source is moved) rubies. intersect at one small point, forming six Because tube-like structures that extend triangular ruby sectors. In many specimens, into the gem-quality ruby sectors are almost however, the arms extend outward from a colourless, and the calcite and dolomite hexagonal central core, producing six inclusions are iron-free, it was concluded trapezohedral ruby areas. The cores are that the yellow colour of the arms and some usually opaque yellow or black, but cores must be due to intense weathering and transparent red central areas are also secondary iron staining of the cavities and present occasionally. tubes. This interpretation was supported by © Gemmological Association and Gem Testing Laboratory of Great Britain ISSN: 135^4565 290 ~Q s Table 1. Chemical zoning? of trapiche rubies • "5 5 u s a S b o Sample. description ZOl1il1gil1 Mg AI Si Ca Ti V Cr Fe A Six-rayed star with sharp yellowish-white Triangular ruby sectors z arms intersecting at one small point Yellowish-white arms + ++ + B Six-rayed star with sharp yellOW arms Triangular ruby sectors z intersecting at one small point Yellow arms ++ ++ u C Six-rayed star with sharp yeUow arms, Trapezoidal ruby sectors black core Black core + +++ + • ++ Yellow arms + ++ + • +++ D Six-rayed star with yelJow arms that widen Trapezoidal ruby sectors + + + + + + + + + toward the edge, black core Black core + ++ + • +++ + + + YeUowarms + ++ + • +++ w "8 E Six-rayed star with zoned, sharp yellowish- Trapezoidal ruby sectors z : + + i i whlte (inner part) to yeUow (outer part) B.1 ack core ++ + + + + + + o U N ^ arms, black core YeUowish-white to yellow arms ++ +or++ N - ' (z) • F Six-rayed star with thin yellow9 arms Trapezoidal ruby sectors z 9 without distinct, continuous bowldaries Red core + / . to the host, small red core Yellow arms + + ':-< Gemm. , 2998, *! I •4 •4 • • I J li « §« C u £ o S g. .... H s S c I D 3 3 s m o o < 6 . 5 . u S smaller concentration than in the six trigonal or trapezohedralP ruby sectors ::g * si s * s s s ,00 J " o > X . 3 s s 8 . 26 much smaller G concentration than in the six trigonal or trapezohedral ruby sectors .S c * 8 c N s S g 2 4 , ,~ | 5, P + higher concentrationu than in the six trigonal or trapezohedral ruby sectors a . *L 5 X I t £ 8 8 o s 5 9 S 0 * O ^ S 3 * 3 8 ,CJ1 s 3 M 0 S -. O N w 289-30 * * ++ much higher concentration than in the six trigonal or trapezohedral ruby ^ sectors g 3 * N + + + S § 8 • C O • 00 N > s . +++ very much higher concentration -S than in the six trigonal or trapezohedral ruby sectors 5 £ 8 S i w * 8 z zoning from fc centre to rim ! s 1 T I x P ^ a e o < o o ;::; 3 n u not observable inj small concentrations due to an overlap of VKa with TiK~ d 291 b Figure la to f:f: Hexagonal cross-sections of six trapiche rubies, samples A to F; the arms of thethe fixed six-rayed stars intersect in a small centralcentral point (a,b) oror extend extend outward outward from from thethe comers corners of of a a hexagonal blackblack (c,d,e) (cj&je) or orred red (f) (f)core. core. The The arms arms of of the stars are yellowish-whiteyellowish-white (a),(a), yellowyellow (b,c,d,f)(b,c4,f) or zoned yellowish-white in an inner part and yellow c in an outer part of the sample (e). Sizes of the samples are 4.8 mm (a), 3.3 mm (b), 3.2 mm (c), 4.1 mmmm (d),(d), 4.24.2 mm mm (e),(e), and and 4.5 4.5 mm mm x x 5.0 5.0 mm mm (fJ. (f). Element mapping of trapiche rubiesrubies X-ray fluorescence analyses of selected The application of the two conventional trapiche ruby areas with or without a part of methods described, however, is unable to a yellow arm. provide two-dimensional information about Two methods were applied to determine element concentrations and chemical the chemical properties of trapiche rubies by variability in minerals, which is of great Schmetzer et al. (1996a) providing analytical interest in trapiche rubies. data that represent different-size areas The present paper describes two different within a sample. X-ray fluorescence analysis techniques for the determination of two- reveals an average composition of that part dimensional element maps in trapiche rubies, of the ruby in an area exposed to the X-ray which have been only rarely applied to the beam that can be measured in the range of characterization of gem materials. Using square millimetres. The electron microprobe, trapiche rubies as an example, the techniques on the other hand, is able to analyse much described are able to fill the gap,between smaller areas with diameters down to about conventional X-ray fluorescence analysis and one micrometre. conventional electron microprobe techniques. The chemical variability of a mineralogical sample is, in general, detectable by electron Materials microprobe using two conventional techniques. Preparing X-ray scanning images For the present study six slices of trapiche for selected elements, the intensities of single rubies were cut in a direction perpendicular spots within an image of the area covered by to the c-axis of the corundum crystals.