Pelites

Pelites are metamorphic rocks derived from pelitic protoliths, meaning clay- or mud-rich sediments such as shales and mudstones. They belong to the aluminous group of metamorphic rocks and are commonly formed during burial and heating in continental crust, often in orogenic belts associated with mountain building. The term pelite also refers to rocks in the pelitic suite, including slate, phyllite, and schist derived from such parent materials.

The mineralogy of pelites reflects metamorphic grade. In low-grade rocks, slate and phyllite typically contain muscovite and chlorite with quartz and feldspars, giving a slaty or glossy sheen in phyllites. As metamorphism increases, the rocks become schists with growth of platy minerals like biotite and muscovite and often garnet. At still higher temperatures and pressures, pelites can develop heavy aluminum silicate minerals such as kyanite, sillimanite, or cordierite, and may host garnet or staurolite. Accessory minerals can include zircon, tourmaline, and opaque minerals. The textures evolve from planar cleavage in slate to a layered or schistose fabric in phyllite and schist.

Pelites serve as key records of metamorphic conditions. The progression of mineral assemblages tracks pressure–temperature changes, and pelitic rocks can reach greenschist, amphibolite, granulite, or blueschist facies under varying tectonic settings. They are widespread in many mountain belts and are commonly studied to understand metamorphic histories and crustal processes.