A model for the interpretation of Mössbauer spectra of muscovite

The literature Mössbauer parameters for a representative collection of muscovites, which were interpreted assuming the possible coexistence of trans- and cis-vacant sheets, were used to prove an alternative interpretation in terms of the local structure. Crystal-chemical models including the assignment of the local cation arrangements (LCA) around Fe³⁺ and Fe²⁺ to predicted and tentative quadrupole splitting values, respectively, and the LCA occurrence probabilities provided by the simulation of two-dimensional cation distribution (CD) were used. The obtained CD reconstructions in dioctahedral trans-vacant sheets correspond to the two types of muscovites revealed by Mössbauer spectroscopy. The main contributors into type-I muscovite are the 2R²⁺Al LCAs around Fe²⁺ (R²⁺ stands for Fe²⁺ and Mg) whereas in type-II muscovite the 3Al and 2AlFe³⁺ LCAs are more important. This implies a more ordered CD in type-II muscovites than that in type-I muscovites from the point of view of Pauling’s principle of the homogeneous dispersion of charge.