The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellarminerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is produced. By definition, schist contains more than 50% platy and elongated minerals, often finely interleaved with quartz and feldspar.

Schist is most notable in caves where it is known that over time water runs down the rocks wearing them away to form the cave. Schist lay superior to other rocks found in caves because it is the predominant rock that does not get weared away by the water.