Use of diffraction and Mössbauer methods for the structural and crystallochemical characterization of nontronites

The aim of this work is the study of the order-disorder distribution of the Fe³⁺ cations in a dioctahedral smectite: the Garfield nontronite. The structural characteristics have been determined by selected-area electron diffraction, oblique texture electron diffraction and X-ray diffraction. These methods lead to the conclusion that the octahedral vacancies are in trans positions and that part of the Fe^{3 +} ions is occupying the tetrahedral sites. The Mössbauer spectra of the nontronite were decomposed into four doublets. According to the determined structural characteristics, these doublets are interpreted in terms of trans vacant octahedral positions.