n.a
term for several types of
rock that are found in
parallel horizontal layers and split easily into
thin sheets. The
word schist comes from Greek schistos, meaning split. Schists are formed when great
pressure and
heat deep below the Earth's surface alter the shape and mineral content of
solid rock. They are often named after the mineral they contain; for
example, a schist made mostly of graphite (the soft, black material that is used in pencils), is called graphite schist.