Computer simulation of octahedral cation distribution and interpretation of the Mössbauer 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 Mössbauer and IR spectroscopies and the original approach. The approach is based on individual quadrupole splittings Δ_i^pred 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 Δ _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 Δ_i ^tent 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 Δ_i^tent for Fe²⁺ combined with Δ_i^pred for Fe³⁺ and with the new CD simulation program provide an additional means for controlling the CD reconstruction.