Computer simulation of octahedral cation distribution and interpretation of the Mossbauer Fe2+ components in dioctahedral trans-vacant micas

Cation distributions (CDs) in the representative collection of trans-vacant dioctahedral celadonites, glauconites and ferriillites were investigated using Mossbauer and IR spectroscopies and the original approach. The approach is based on individual quadrupole splittings Δ i pred for Fe 3+ in possible local cation arrangements around Fe 3+ , 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 Δ j of Fe 2+ derived from computer fits to the corresponding spectra and cation composition of local cation arrangements around Fe 2+ with their occurrence probabilities. Basing on this correlations, a total of eight individual Δ tent for Fe 2+ 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 Fe 3+ and Fe 2+ and implies a direct dependence of the Fe 2+ quadrupole splitting on the structural distortion at Fe 2+ site. The set of Δ i tent for Fe 2+ combined with Δ i pred for Fe 3+ and with the new CD simulation program provide an additional means for controlling the CD reconstruction.