Medium- to coarse-grained, mica-bearing metamorphic rock with well-developed foliation termed schistosity. Schist is derived primarily from fine-grained, mica-bearing rocks such as shales and slates. The schistosity is formed by rotation, recrystallization, and new growth of mica; it is deformational in origin. The planar to wavy foliation is defined by the strong preferred orientation of platy minerals, primarily muscovite, biotite, and chlorite. The relatively large grain size of these minerals (up to centimeters) produces the characteristic strong reflection when light shines on the rock.