The crystal-chemistry of riebeckite

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Marco E. Ciriotti
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The crystal-chemistry of riebeckite

Messaggio da Marco E. Ciriotti » sab 21 ott, 2017 13:20

Prossima pubblicazione.

▪ Susta, U., Della Ventura, G., Hawthorne, F.C., Abdu, Y.A., Day, M.C., Mihailova, B., Oberti, R. (2018): The crystal-chemistry of riebeckite, ideally Na2(Fe2+3Fe3+2)Si8O22(OH)2: a multi-technique study. Mineralogical Magazine, 82, (in press).

In this work we report on a complete crystal-chemical characterization of a near end member riebeckite from Malawi, and use the available data to critically compare information obtained from different analytical methods. The sample occurs as well-formed and very large 30 single crystals in pegmatitic rocks. Accurate site-populations were determined by combining single-crystal structure refinement (SREF) and electron microprobe analysis (EMPA). Fe3+/Fe2+ ratio was obtained from Mössbauer spectroscopy. Li was quantified by Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA ICP-MS). Fourier-Transform Infrared (FTIR) spectra, collected both on powders and single crystals, are 35 presented and discussed. FTIR spectra in the NIR region are also presented for the first time for this amphibole. The FTIR data are compatible with complete local ordering of A cations close to F, and complete Fe2+/Mg disorder at M(1,3). Polarized Raman-scattering data collected from single crystals confirm this conclusion. In addition, it was found that FTIR data collected on powders provide the best agreement with the site occupancies derived from chemical (EMP and LA-ICP-MS) and crystal-chemical data, possibly because they do not depend on experimental issues such as orientation and polarization.
Marco E. Ciriotti

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