A suite of mica schists from the staurolite zone was studied in detail. Phase rule considerations and distribution relations indicate that chemical equilibrium was attained within the sample volume. Iron-magnesium ratios of the silicates vary greatly, and correlate with rock ferrous-ferric ratio, as does the oxide mineral mode. Rock oxidation state varies locally, and is probably dependent on the composition of the original sediment. Distribution coefficients for Fe, Mg, and Mn among garnet, biotote, and staurolite show no vaiation attributable to temperature. Partition of Fe and Mg between staurolite and biotite is regular, but non-ideal. The staurolite structure permits only limited (15–35 percent) substitution of Mg for Fe.
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Hounslow et al. (1967) studied this question.