Comparison between the quasi-continuous quadrupole splitting distributions (QSD) for Mössbauer spectra of glauconites and the QSD-profiles simulated on the basis of crystal-chemical model

Structural peculiarities of Fe3+-rich dioctahedral mica, glauconite, such as a wide variety of isomorphous octahedral cation substitutions (Al, Fe3+ Fe2+ Mg) and the occurrence of these cations in cis-sites only, make it possible to consider glauconites as model locally inhomogeneous objects. To fit room and liquid-nitrogen Mössbauer spectra of two glauconite samples of close compositions with unusually low Fe3+/Fe2+ ratios, reconstruction of quadrupole splitting distributions (QSD) in terms of quasi-continuous model-independent approach was applied. Interpretation of the obtained QSDexps became possible owing to application of a crystal-chemical model (CCM) taking account of the effects of the local structural and chemical heterogeneity of layer silicates. The main parameters of the CCM are individual quadrupole splittings, Δi, for Fe3+ Fe2+ in different local cationic arrangements (LCAs) having the occurrence probabilities, wi, provided by two-dimensional simulation of the cation distribution (CD). The agreement between CD reconstructions, the QSDsim profiles simulated on the basis of the CCM parameters and the QSDexps provided, first, the corroboration of the Δipred values for Fe3+; second, the refinement of the Δiref values for Fe2+; and third, revealing the difference in the octahedral cation distributions for the studied glauconites.