Collier's New Encyclopedia (1921)/Mica Schist

MICA SCHIST (shist), or MICA SLATE, a slaty metamorphic rock composed of mica and quartz. The mica is usually muscovite (potash mica), though sometimes it is biolite (magnesian mica). The rock usually splits along the micaceous folia. Occasionally mica seems to constitute the whole mass of the rock. Next to gneiss, mica schist is the most common metamorphic rock.