Distribution of elements in coexisting minerals and the problem of chemical disequilibrium in metamorphosed basic rocks

Distribution of elements in coexisting minerals—biotite, hornblende, augite, hypersthene and plagioclase in charnockitic rocks of West Uusimaa Complex, Finland, is mostly orderly indicating a close approach to chemical equilibrium. The distribution of iron and magnesium in coexisting hornblende and pyroxenes of basic charnockites and other rocks of granulite facies from several different areas is also orderly but the variation in the fugacities of H₂O and H₂ may cause a disorderly distribution locally in some rocks. The probable oxidation or reduction reactions are discussed on the basis of thermochemical and mineralchemical data.