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The Texture and Chemical Composition of Trapiche Ruby from Khoan Thong, Luc Yen Mining District, Northern Vietnam

Journal of gemmology (1986), 2019-01, Vol.36 (8), p.726-746 [Peer Reviewed Journal]

COPYRIGHT 2019 Gem-A, The Gemmological Association of Great Britain ;2019 The Gemmological Association of Great Britain ;ISSN: 1355-4565 ;EISSN: 2632-1718 ;DOI: 10.15506/JoG.2019.36.8.726

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  • Title:
    The Texture and Chemical Composition of Trapiche Ruby from Khoan Thong, Luc Yen Mining District, Northern Vietnam
  • Author: Pignatelli, Isabella ; Giuliani, Gaston ; Morlot, Christophe ; Van Long, Pham
  • Subjects: Boundaries ; Calcite ; Composition ; Crystals ; Dolomite ; Fluids ; Gemology ; Identification and classification ; Iron ; Magma ; Marble ; Metamorphism ; Mineralogy ; Mines ; Mining ; Natural history ; Properties ; Pyrite ; Rubies ; Tomography
  • Is Part Of: Journal of gemmology (1986), 2019-01, Vol.36 (8), p.726-746
  • Description: The trapiche texture and chemical composition of two rubies from the Khoan Thong placer in northern Vietnam were examined by X-ray computed tomography, scanning electron microscopy and electron microprobe analysis. Their texture is similar to that of some Burmese trapiche rubies, with inclusion-rich sector boundaries intersecting at a small central point and a significant concentration of elongated tube-like voids in growth sectors. The most common inclusions are anorthite and margarite; the latter formed by destabilisation of both ruby and anorthite during retrograde metamorphism. The chemical composition of the samples plots in the field of Vietnamese alluvial and primary marble-hosted deposits, although differences in [Fe.sub.2][O.sub.3], Ti[O.sub.2] and [Cr.sub.2][O.sub.3] contents may distinguish trapiche rubies from various mining areas in Vietnam. Their composition differs from that of Burmese trapiche rubies by a higher [Fe.sub.2][O.sub.3]/Ti[O.sub.2] ratio and a lower [Cr.sub.2][O.sub.3] content. Vietnamese trapiche rubies formed in the same geological environment as non-trapiche ones, under metamorphic conditions prevailing for the Himalayan orogenesis. In this geological context, localised fluid pressure variations and hydraulic fracturing caused changes in the driving force of crystallisation, favouring the development of the trapiche texture.
  • Publisher: London: Gem-A, The Gemmological Association of Great Britain
  • Language: English
  • Identifier: ISSN: 1355-4565
    EISSN: 2632-1718
    DOI: 10.15506/JoG.2019.36.8.726
  • Source: ProQuest Central

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