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The distribution coefficient, KD ≡ (Mg/Fe)garnet/(Mg/Fe)biotite, has been calculated for seventy garnet-biotite pairs from samples of known mineral assemblage and from a range of metamorphic grade. This distribution coefficient depends upon the metamorphic grade, but it is also dependent upon the Mn content of garnet and upon the detailed mineral assemblage. For a single assemblage from a given metamorphic grade the distribution coefficient is reduced by about 0.007 per 1 atom per cent of (Mn/Mn + Mg + Fe)garnet. Values of KD for isogradic assemblages differ by about 0.045. The distribution coefficient for different metamorphic grades is compared by projection to an arbitrary zero value of (Mn/Mn + Mg + Fe)garnet. KD for garnet-zone rocks is about 0.2, for staurolite-zone rocks about 0.215, for kyanite-zone rocks about 0.23, and for sillimanite-K-feldspar-zone rocks about 0.3-0.37.
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A. L. Albee (1965) studied this question.
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