A regional metamorphic rock of pelitic (see pelite) composition which displays a schistosity. Schists are coarser-grained than phyllites, having a grain size greater than 1 mm. The minerals defining the schistosity may be muscovite mica, biotite mica, and/or elongate quartz, depending on the composition and the pressure and temperature of formation. When a basic igneous rock is metamorphosed it forms a hornblende-schist (amphibolite) or greenschist if it contains a planar fabric, or a greenstone if no fabric is present. Thus in this latter context ‘schist’ refers to the fabric component and not to the overall rock type.