An 57Fe Mo ¨ssbauer spectral study of vermiculitization in the Palabora Complex, Republic of South Africa
Two phlogopite, two mixed-layer phlogopite-vermiculite, and two vermiculite samples collected from the Palabora Complex of South Africa have been investigated at 295 K by X-ray diffraction, chemical analysis, and Mössbauer spectroscopy. In addition the temperature dependence of the Mössbauer spectra has been measured between 95 and 295 K for one phlogopite and one mixed-layer sample. The results of the chemical analyses and the Mo ¨ssbauer spectra improve our knowledge of the vermiculitization process in the Palabora Complex. Both techniques indicate oxidation of the Fe ions during the sequence: phlogopite → mixed-layer → vermiculite. Further, the Mössbauer spectra indicate that Fe oxidation occurs mainly in the octahedral sites and suggest that migration and oxidation of the Fe2+ ions from the octahedral sites to the tetrahedral sites may occur during the transformation of phlogopite into a mixed-layer phase. Finally, the vermiculitization process involves both Fe oxidation and loss of K with a concomitant increase in the Mg content.
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Document Type: Research Article
Publication date: 2000-09-01