Abstract
The crystal structure of julgoldite-Fe 3+ from Bombay, India, was investigated by 57 Fe Mössbauer spectroscopy and synchrotron X-ray powder diffraction. Only ferric iron was detected in the Mössbauer measurements and it occurs at two different octahedral sites in the atomic ratio 20:80. Based on Rietveld refinements, the Fe 3+ cations are located at the X- and Y-octahedral sites with atomic percentages of about 25% and 75%, respectively. The resulting chemical formula of the Bombay julgoldite sample is Ca 8 (Fe 3+ 2.7 Al 1.1 Mg 0.2 )(Fe 3+ 8.0 )Si 12 O 42 (OH) 14 . The oxidation state of Fe is not the same as that arrived at through simple crystal-chemical considerations. Such analysis cannot give quantitative results for the valence state of mixed-valence cations in pumpellyite-type minerals and their intracrystalline partitioning behavior. Assignments of the Mössbauer absorption doublets and an analysis of Fe-intracrystalline partitioning behavior are discussed with reference to previous works on different pumpellyite-type minerals.
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