COMPUTER SIMULATION OF OCTAHEDRAL CATION DISTRIBUTION AND INTERPRETATION OF THE MöSSBAUER FE2+ COMPONENTS IN DIOCTAHEDRAL TRANS-VACANT MICAS

Abstract

Cation distributions (CDs) in the representative collection of trans-vacant dioctahedral celadonites, glauconites and ferriillites were investigated using Mössbauer and IR spectroscopies and the original approach. The approach is based on individual quadrupole splittings ipred for Fe3+ in possible local cation arrangements around Fe3+, and on a computer simulation of two-dimentional CDs using the IR data in the OH stretching vibration region. The resulting CDs were next used to make correlations between j of Fe2+ derived from computer fits to the corresponding spectra and cation composition of local cation arrangements around Fe2+ with their occurrence probabilities. Basing on this correlations, a total of eight individual itent for Fe2+ referred as "tentative" have been derived. The order of local cation arrangements in terms of increasing quadrupole splitting was found to be the same both for Fe3+ and Fe2+ and implies a direct dependence of the Fe2+ quadrupole splitting on the structural distortion at Fe2+ site. The set of itent for Fe2+ combined with ipred for Fe3+ and with the new CD simulation program provide an additional means for controlling the CD reconstruction.