Low-temperature (down to 4.2 K) 57Fe Mössbauer spectra have been taken of “ferrifayalites (Fe3+-rich fayalites) from three localities. Room-temperature spectra show two pairs of peaks, due to ferrous and ferric ions in octahedral coordination. The peaks due to ferrous iron split at low temperatures to form a pattern consistent with that of “normal” ferrous fayalite. The peaks due to ferric iron split independently to form at least one hyperfine sextet.

Based on these observations, a two-phase structure for “ferrifayalite” is proposed, in which ferrifayalite” is composed of an intergrowth of “normal” ferrous fayalite and laihunite, Fe2+Fe23+(SiO4)2. This model is supported by scanning electron microscope (SEM) photographs showing the two phases.

In addition, infrared spectra and plots of M1 and M2 octahedra size vs. cation radius were used to estimate site occupancy of laihunite. The M2 site was found to contain ferric ions alone, whereas the M1 site contains a mixture of ferrous ions and vacancies.

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