KINETICS OF THE (FE(2-)MICA-](FE(3+)+ O2-)MICA +H OXIDATION REACTION IN BULK SINGLE-CRYSTAL BIOTITE STUDIED BY MOSSBAUER-SPECTROSCOPY()+ OH)

We report the first kinetic study of iron oxidation in a mica. Large s ingly-crystal biotite wafers were heated in air to various temperature s and for various times. Room temperature Fe-57 Mossbauer spectroscopy was used to quantify the resulting Fe2+ and Fe3+ amounts. A simple ac tivation model is consistent with the measurements and gives an activa tion energy of e(b) = 2.36 eV and an attempt frequency of f(o) = 2.9 x 10)(7) Hz. We are lead to propose that, iron oxidation and ordinary d ehydroxylation have the same rate limiting step: local dissociation of an OH group as OH- --> O2- + H+. In oxidation this is followed by Fe2 + + H+ --> Fe3+ + H whereas in dehydroxylation it is followed by OH-H+ --> H2O.