A Comparative X-ray Diffraction, Mössbauer and NMR Spectroscopic Study of the Vermiculites from Béni Bousera, Morocco and Palabora, Republic of South Africa

Five vermiculite samples collected from Béni Bousera, Morocco and four from Palabora. South Africa were investigated by X-ray diffraction, chemical analysis. ⁵⁷ Fe Mössbauer spectroscopy, and ²⁷ Al magic angle spinning nuclear magnetic resonance. The X-ray diffraction studies indicate that all vermiculites have very similar crystallographic parameters. The chemical analyses and the NMR spectra indicate that the Béni Bousera vermiculites contain Al ³ cations in both octahedral and tetrahedral sheets and the Palabora vermiculites contain Al ³ in the tetrahedral sheet. The Mössbauer spectra indicate that the Béni Bousera vermiculites contain more Fe ² cations than the Palabora vermiculites and do not contain tetrahedral Fe ² cations. The different cation compositions and distribution in the two sets of vermiculites may result from different parent minerals, i.e. chlorite in the case of Béni Bousera and phlogopite in the case of Palabora, and different genetic processes, i.e. weathering in Béni Bousera and hydrothermal alteration in Palabora.