Pelitische

Pelitische is an adjective used in geology to describe rocks derived from pelites, a class of metamorphic rocks formed from clay-rich sediments such as mudstone or shale. The term is commonly used in German and Dutch-speaking literature as the adjectival form of pelite.

Pelitische rocks form under regional metamorphism, progressing from low-grade to high-grade conditions. Early-stage pelites yield slate with fine slatey foliation, which can develop into phyllite and then schist as metamorphism increases. At higher temperatures and pressures, pelitic rocks may become garnet-bearing schists or granulites. The metamorphic mineral assemblages typically include platy minerals such as muscovite and chlorite at lower grades, with biotite, garnet, and, in higher-grade rocks, sillimanite, kyanite, or cordierite appearing in the sequence.

Texture and structure are characteristic: pelitic rocks are generally foliated, showing a preferred alignment of platy minerals (slaty cleavage, phyllitic sheen, or schistosity). They often display chemical and mineralogical layering that records differential metamorphic reactions and deformation.

Pelitic rocks are contrasted with psammitic rocks, which originate from quartz- and feldspar-rich sediments and tend to form different metamorphic assemblages. Pelitische formations are important in crustal development studies, as their mineral assemblages and textures preserve pressure–temperature histories that illuminate regional tectonics, crustal thickening, and metamorphic facies transitions.

Examples include pelitic slate, pelitic phyllite, and pelitic schist, as well as garnet- or cordierite-bearing pelitic gneiss at higher metamorphic grades.