The fingerprint of imperial topaz from Ouro Preto region (Minas Gerais state, Brazil) based on cathodoluminescence properties and composition
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2017
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A study of the cathodoluminescence (CL) properties of imperial topaz from Ouro Preto region (Minas
Gerais state, Brazil) and its relation with trace-element composition was conducted, using scanning electron
microscope cathodoluminescence (SEM-CL), optical microscope cathodoluminescence (OM-CL),
cathodoluminescence-spectrometry (CL-spectrometry), electron microprobe analysis (EMPA), laser
ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) and Raman spectrometry. Each
analytical technique allowed characterization of the imperial topaz fingerprint. SEM-CL panchromatic
images show different crystal growth and resorption events in imperial topaz crystals. Colour CL images
indicate only blue to violet emissions. The CL-spectra indicate a broad emission band with low intensity
peak at ∼417 nm and a broad emission band with high intensity and major peaks at 685, 698, 711 and
733 nm. The EMPA indicates high OH content, in which the OH/(OH + F) ratio ranges between 0.35–0.43
(0.72 ≤ OH ≤ 0.86 apfu). High Cu and Zn concentrations (LA-ICP-MS) were measured in the high
luminescence areas of SEM-CL images, suggesting both elements as CL-activators in imperial topaz.
Raman and CL-spectra indicate high Cr concentrations, corroborated by EMPA and LA-ICP-MS results.
The high Cr caused strong luminescence intensities that enabled their superimposition over the OH
stretching mode (∼3650 cm–1) of topaz in all Raman spectra. Among trace elements, the concentrations of
Ti, V, Cr, Mn, Fe, Cu, Zn, Ga and Ge provide the fingerprint of imperial topaz.
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Trace elements
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ARAÚJO, T. G. R. de. et al. The fingerprint of imperial topaz from Ouro Preto region (Minas Gerais state, Brazil) based on cathodoluminescence properties and composition. Mineralogical Magazine, v. 82, p. 943-960, 2018. Disponível em: <https://www.cambridge.org/core/journals/mineralogical-magazine/article/fingerprint-of-imperial-topaz-from-ouro-preto-region-minas-gerais-state-brazil-based-on-cathodoluminescence-properties-and-composition/18A550A73C41BB7E157AB419C7F5B732>. Acesso em: 08 fev. 2019.