Vigier, M. & Fritsch, E. (2020) Pink Axinite from Merelani, Tanzania: Origin of Colour and Luminescence. Journ of Gemm, 37 192–205.
Added by: Richard Baschera (2020-07-10 08:09:58) Last edited by: Richard Baschera (2020-07-10 08:15:53)
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Numéro d'identification (ISBN etc.): 13554565
Clé BibTeX: Vigier2020
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Créateurs: Fritsch, Vigier
Collection: Journ of Gemm
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Two pink axinites from Merelani, Tanzania, were characterised with standard gemmological techniques, energy-dispersive spectroscopy, and UV-Vis-NIR, Raman and luminescence spectroscopy. We compared them to three other samples from Merelani (pinkish orange, blue and near-colourless) and one brown axinite from Oisans, France. Chemical analysis revealed that the two pink axinites correspond to axinite-(Mg). UV-Vis-NIR spectroscopy revealed that the origin of the pink colouration is a large, asymmetric broad band centred at about 560 nm. Its position and shape are typical for Mn3+. Manganese is also present in both samples as Mn2+, and we surmise that natural radiation from nearby minerals converted some Mn2+ into Mn3+. The orange luminescence of the axinites (weaker under short-wave UV radiation) is related to a broad emission band at 631 nm caused by Mn2+, and a more unusual red luminescence is associated with features at 688 and 694 nm attributed to Cr3+. Raman spectroscopy showed slight variations between the different axinite species, but further research is needed to associate each axinite end member with its characteristic Raman spectrum.