Abstract
A homogeneous megacryst of schorlomite was investigated to determine the valence states of Fe and Ti and the crystallographic sites occupied by these elements. The chemical composition of the specimen was analyzed by electron microprobe, wet-chemical analysis, FTIR, and INAA. The results from X-ray absorption near-edge structure spectroscopy (XANES) are consistent with exclusively Ti4+ occupying the octahedral site only. The tetrahedral site is deficient in Si and the results of low-temperature 57Fe Mössbauer spectroscopy indicate that the remainder of the site is occupied by Fe3+ and substantial Fe2+. A spin-allowed intensified crystal-field transition of [4]Fe2+ is present in the near-infrared spectrum. The optical absorption spectrum is dominated by an intense band centered at 500 nm with a full width of 8000 cm−1 at half maximum peak height; this band is assigned to an Fe2+-Ti4+ intervalence charge transfer transition between [4]Fe2+ and [6]Ti. The cation site occupancies in this specimen of schorlomite can be expressed by the following formula: .
