pelite

Pelite is a fine-grained metamorphic rock or rock group derived from clay-rich sedimentary rocks, such as mudstones and shales. The name reflects its aluminous chemistry and abundance of clay minerals. In metamorphic rocks, pelites typically retain the original fine texture but develop a platy, fissile fabric dominated by phyllosilicates.

Mineralogy and metamorphism vary with grade. Low-grade pelites commonly contain muscovite, chlorite, and sericite (fine mica), along with quartz and feldspar. With increasing temperature and pressure, dehydration reactions produce mineral assemblages that may include garnet, biotite, staurolite, and, at higher grades, kyanite, sillimanite, or cordierite. In the highest-grade regions, some pelites develop granulite-facies minerals such as orthopyroxene. These mineralogical changes reflect regional metamorphic conditions rather than a single path.

Petrologically, pelites are distinguished from pelitic rocks derived from other protoliths by their high aluminum content and clay-rich composition. They form the dominant metamorphic products of mudstones and shales and are commonly represented by lithologies such as slates, phyllites, and schists as metamorphism progresses. The pelite facies describes a sequence of chemical and mineralogical changes typical of mudrock-derived rocks subjected to increasing temperature and pressure in regional metamorphism.

Occurrence and significance: Pelites occur worldwide in continental collision zones and accretionary orogens, where mudstones and shales undergo regional metamorphism. Studying pelites provides insights into metamorphic conditions, fluid activity, and tectonic history, helping reconstruct the thermal and pressure evolution of metamorphic belts.