SOME PETROLOGICAL ASPECTS ON STILPNOMELANE IN GLAUCOPHANITIC METAMORPHIC ROCKS

Abstract

Under the glaucophanitic metamorphic conditions, stilpnomelane appears in schists whose grade ranges from the pumpellyite zone to the biotite zone. The parageneses of stilpnomelane in these schists are rather simple, and the mineral is associated commonly with quartz, chlorite and calcite and rarely with epidote, pumpellyite and actinolite. The apparent wide range of chemical and mineralogical compositions of stilpnomelane-bearing schists is due to small-scale heterogeneity of rocks, but not due to their suitable bulk chemical composition.