A comparative X-ray diffraction, Mossbauer and NMR spectroscopic study of the vermiculites from Beni Bousera, Morocco and Palabora, Republic of South Africa

Five vermiculite samples collected from Beni Bousera, Morocco and four from Palabora, South Africa were investigated by X-ray diffraction, chemical ana lysis, Fe-57 Mossbauer spectroscopy, and Al-27 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 Beni Bousera vermiculites contain Al3+ cations in both octahedral and tetrahedral sheets and the Palabora vermiculites contain Al3+ in the tetrahedral sheet. The Mossbauer spectra indicate that the Beni Bousera vermiculites contain more Fe2+ cations than the Palabora vermiculites and do not contain tetrahedral Fe3+ 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 Beni Bousera and phlogopite in the case of Palabora, and different genetic processes, i.e. weathering in Beni Bousera and hydrothermal alteration in Palabora.