Schist

Schist, term applied to any of several metamorphic rocks in which the crystals of the predominating mineral are aligned in parallel layers, forming a large number of close, well-developed foliations. Schistose rocks are easily broken along a lamination, or schistosity, into thin, flaky plates. The various schistose rocks are named and characterized according to the predominating mineral that produces the foliation.

Among the important schists are mica schist, hornblende schist, chlorite schist, and talc schist. Quartz is usually the predominant secondary mineral. The most common schistose rock and, second to gneiss, the most common metamorphic rock is mica schist. Mica schist is composed of mica, usually in the form of biotite or muscovite, and smaller amounts of quartz. Schists that contain important accessory minerals are characterized by the accessory mineral. Garnet-mica schist is a mica schist containing crystals of garnet.