Schist

Schist is a medium- to coarse-grained metamorphic rock whose platy minerals align in layers, producing a pronounced foliated texture. Its visible mineral grains distinguish it from finer-grained foliated rocks.

Foliation (geology): A planar arrangement of minerals or compositional layers in a rock, commonly produced during metamorphism. Schist’s defining texture is a particularly pronounced form of foliation.
Differential stress: Stress that differs by direction, producing unequal forces within a material. Directed stress can rotate or align platy minerals as schist deforms.
Mica schist: A schist dominated by visible mica, commonly with quartz and other minerals. Abundant aligned mica flakes give this common variety its characteristic sheen.
Slate: A fine-grained metamorphic rock that splits into thin sheets along cleavage planes. Slate has a finer texture and slaty cleavage rather than schist’s visible grains.
Dimension stone: Natural stone quarried and cut to specified dimensions for construction or decoration. Some schists are quarried for uses that exploit their color and layered appearance.
Mica: A group of sheet silicate minerals that split readily into thin, flexible layers. Mica commonly forms the aligned, reflective flakes visible in schist.
Recrystallization (geology): The growth or reorganization of mineral grains in a solid rock during changing conditions. Recrystallization produces schist’s coarse grains without melting the rock.
Garnet schist: A schist containing conspicuous garnet crystals in a foliated mineral matrix. Its garnets can record metamorphic growth within the schist’s finer matrix.
Phyllite: A fine- to medium-grained foliated metamorphic rock with a silky sheen and wavy surfaces. Phyllite is finer-grained than schist, marking a textural step in metamorphic progression.
Geologic mapping: The recording and interpretation of geological features across an area, commonly on maps. Schist’s foliation and mineral assemblages help map metamorphic zones and deformation.

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