On dehydroxylation mechanisms of a biotite in vacuo and in oxygen

Abstract

The dehydroxylation mechanisms of a biotite in the temperature range 300–800° C at controlled oxygen pressures were studied by infrared (IR) and Mossbauer spectroscopies. At low pressure, the lack of O2 delays the oxidation of Fe+2 and simultaneous loss of hydrogen but favours the loss of OH associated with octahedral vacancies in comparison with heat treatment in air. Stoichiometrical considerations based on the facts that the octahedral cations are randomly distributed and all Fe+2 is oxidized lead to the conclusion that all the OH groups initially coordinated to Fe+2 must be lost during the oxidation process.