Mössbauer and analytical electron microscopic studies of an unusual orthosilicate: chloritoid

Abstract

Samples of chloritoid (a “layered” orthosilicate) from three distinct geological sources have been examined, both in the naturally occuring and heat-treated forms, by Mössbauer spectroscopy. This technique is shown to elucidate the environment of the iron present constitutionally: there is, for example, only one type of site (with octahedral symmetry in the so-called L₁ layer) occupied by Fe²⁺. The Fe³⁺ ions are present to such a small extent that it did not prove feasible to evaluate their preferred siting. One of the samples (that coming from Rhode Island) displayed an anomalous Fe²⁺ doublet which, by a combination of energy dispersive analysis and electron diffraction (i.e., analytical electron microscopy) and spectrochemical analysis, was shown to arise from minute intergrowths of ilmenite (FeTiO₃).