Abstract

Measurements of polarized absorption spectra of orthopyroxenes and a staurolite together with Mössbauer measurements of orthopyroxenes, show that the earlier interpretation (White and Keester, 1966) of the unpolarized spectra of pyroxenes is incomplete. An alternative explanation of the pyroxene spectra, taking into account the additional information obtained from polarized spectra and Mössbauer measurements, is presented and new band assignments made. The present study does not support the suggestion made by White and Keester that Fe2+ ions occur in tetrahedral coordination substituting for silicon in the SiO4 tetrahedra of pyroxenes. This paper shows that some of the spectral characteristics of Fe2+ in tetrahedral coordination can also be shown by Fe2+ in a very distorted octahedral environment, such as those in many silicate structures. Cation ordering and coordination site symmetry in the orthopyroxene structure are discussed.

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