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granulite A coarse-grained, equigranular metamorphic rock, consisting of quartz, feldspar, and the anhydrous ferromagnesium minerals pyroxene and garnet. There is some confusion over the use of the term granulite, different authors using the name in different ways. Consequently, basic granulites, rich in the ferromagnesium minerals orthopyroxene and clinopyroxene, are better termed ‘pyroxene gneisses’, whilst acid granulites, rich in quartz and feldspar, are better termed ‘charnockitic gneisses’. These rock types are thought to be formed by metamorphism of deep crustal rocks which have suffered earlier dehydration by the removal of a wet granite melt.