Pelitic

Pelitic refers to rocks of clay-rich sedimentary origin that have undergone metamorphism. In metamorphic petrology, pelite denotes the metamorphosed product of mudstones or shales, and it is used to classify metasedimentary rocks by protolith composition. Protoliths are rich in clay minerals such as illite and chlorite and in aluminum-bearing minerals like muscovite, with high aluminum oxide relative to silica and alkalis.

During metamorphism pelites develop mica-rich assemblages. At low metamorphic grade they form slate and phyllite with slaty or phyllosilicate cleavage; at intermediate to high grade they yield mica schists and, in the presence of garnet and aluminosilicate phases, granulite-forming pelites with sillimanite or kyanite. The appearance of garnet, sillimanite, kyanite, staurolite, or cordierite is commonly used to infer pressure–temperature conditions. Chlorite may persist at the lowest grades, giving chlorite-muscovite rocks.

Common pelite lithologies include slate, phyllite, and various mica schist; higher-grade pelites may become garnet-rich mica schists or orthogneiss when recrystallized. In practice, pelites are contrasted with psammites (quartz-rich sediments) and calcsilicate rocks, with the grouping reflecting the original sediment composition rather than metamorphic age.

Pelites often record tectonic histories such as subduction burial and continental collision, and they provide key information about metamorphic facies, dehydration reactions, and fluid-rock interaction during orogenesis.