Abstract
Various indirect approaches have been used to estimate the amount of the oxy end member in biotites. Since this could be used to indicate the formation temperatures and the oxygen fugacities of biotite bearing rocks, its determination requires careful experimental work. The oxidation of the iron micas annite and ferriannite has been studied by Mössbauer effect (ME) and X-ray diffraction (XRD). A model that relates ME parameters to reaction mechanism in biotites has been proposed according to which oxidation at M2 is relatively easier than oxidation at M1, a result which agrees well with the site assignment adopted. Heating synthetic ferriannite at 300° C produced an oxidation ratio that corresponds to the oxy-ferriannite end member where the ME spectra show that the two ferrous peaks are well resolved. Finally, ME and XRD results show that the c-axis decreases by 0.001 Å for every percent oxybiotite added.
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Ferrow, E. Mössbauer and X-ray studies on the oxidation of annite and ferriannite. Phys Chem Minerals 14, 270–275 (1987). https://doi.org/10.1007/BF00307993
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DOI: https://doi.org/10.1007/BF00307993