Crystalline metamorphic rock that has a highly developed tendency to split into layers.
Most schists are composed largely of platy minerals such as muscovite , chlorite , talc , biotite , and graphite . The green colour of many schists and their formation under a certain range of temperature and pressure conditions have led to distinction of the greenschist facies in the mineral facies classification of metamorphic rocks. Schists are usually classified on the basis of their mineralogy, with varietal names that indicate the characteristic mineral present.