Higgins, 1979 sapphirine abstract

Higgins, 1979 sapphirine abstract - Contrib Mineral Petrol...

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Contrib. Mineral. Petrol. 68, 349-356 (1979) Contributions to Mineralogy and Petrology by Springer-Verlag 1979 Sapphirine I Crystal Chemical Contributions John B. Higgins 1 *, Paul H. Ribbe 1, and Richard K. Herd 2 1 Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA 2 Geological Survey of Canada, 601 Booth Street, Ottowa, Canada K1A 0E8 Abstract. Microprobe analyses of 26 natural sapphi- rines from 17 localities indicate that the predominant chemical substitutions in this mineral occur along the solid solution join Vl(Mg,Fe)2 + +wSi4+ =W(A1, Fe) 3+ + WA13 +. Chromium and manganese are minor substituents. Evidence for the substitution Si~Al+l/zMg+l/z vacancy is absent within the limits of analytical error. A partitioning scheme based on electrostatic charge balance considerations has been devised per- mitting calculation of Fe z+ and Fe a+ from total iron content. Results are in good agreement with previous M6ssbauer studies which indicate Fe 3 + is sometimes in octahedral and/or tetrahedral coordination.
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