Abstract
The assignment of spin-allowed Fe2+-bands in orthopyroxene electronic absorption spectra is revised by studying synthetic bronzite (Mg0.8 Fe0.2)2Si2O6, hypersthene (Mg0.5 Fe0.5)2Si2O6 and ferrosilite (Fe2Si2O6). Reheating of bronzite and hypersthene single crystals causes a redistribution of the Fe2+-ions over the M1 and M2 octahedra, which was determined by Mössbauer spectroscopy and correlated to the intensity change of the spin-allowed Fe2+ d-d bands in the polarized absorption spectra. The 11000 cm-1 band is caused by Fe2+ in M1 (5B2g→5A1g) and Fe2+ in M2 (5A1→5A1), the 8500 cm-1 band by Fe2+ in M1 (5B2g→5B1g) and the 5000 cm-1 band by Fe2+ in M2 octahedra (5A1→5B1). The Fe2+-Fe3+ charge transfer band is identified at 12500cm-1 in the spectra of synthetic Fe3+ -Al bearing ferrosilite. This band shows a strong γ-polarization and therefore is caused by Fe2+ -Fe3+-ions in edge-sharing octahedra.
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Steffen, G., Langer, K. & Seifert, F. Polarized electronic absorption spectra of synthetic (Mg, Fe)-orthopyroxenes, ferrosilite and Fe3+-bearing ferrosilite. Phys Chem Minerals 16, 120–129 (1988). https://doi.org/10.1007/BF00203195
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DOI: https://doi.org/10.1007/BF00203195