Octahedral cation distribution in glauconites from Southern Urals by combination of crystal-chemical model and quasi-continuous model-independent quadrupole splitting distributions (QSD) fitted to their Mössbauer spectra

Abstract

Mossbauer spectra of two glauconites, BSH-11 and KUL-1, from the Southern Urals are interpreted by simulation using crystal-chemical modelling and by fitting of quadrupole splitting distribution (QSD). The crystal-chemical modelling is based on X-ray diffraction (XRD) data and includes, as a priori information, individual quadrupole splittings for Fe 3+ and for Fe 2+ that correspond to specific local cation arrangements (LCA) having certain occurrence probabilities. The latter are provided by two-dimensional octahedral cation distribution using integrated infrared optical densities for bands corresponding to the cation pairs bound to the OH groups. Combination of crystal-chemical modelling and quasi-continuous model-independent QSDs fitted to Mossbauer spectra resulted in cation distributions for which R 2+ (Mg, Fe 2+ ) and R 3+ (Al, Fe 3+ ) cations occupy one of two structurally independent cis- sites with equal probabilities. The cation distributions obtained are characterized by Fe-clustering, domain structure, and different trends to homogeneous charge dispersion.