Charnockite

Charnockite is a coarse‑grained metamorphic rock of granulite facies. It is characterized by an essential mineral assemblage of quartz, alkali feldspar (primarily orthoclase or microcline) and plagioclase, plus pyroxene (usually orthopyroxene). Accessory minerals may include biotite, garnet, rutile, zircon, and ilmenite. The texture is typically holocrystalline and equigranular, though some varieties show porphyroblastic features with larger crystals of garnet or pyroxene.

Mineral chemistry and texture distinguish charnockite from typical granites or other granitoids. The presence of pyroxene with alkali feldspar and quartz is diagnostic, and many samples also show evidence of high-grade metamorphism, such as strong foliation and irregular recrystallization.

Formation and metamorphic conditions are linked to high-temperature, medium- to high-pressure regimes of granulite facies metamorphism. Charnockites are thought to form by high-temperature metamorphism of preexisting crustal rocks, sometimes involving partial melting and melt-related processes that yield an orthopyroxene-bearing assemblage. They often occur in deeply buried crustal domains and may be associated with migmatites and other high-grade rocks.

Geographic distribution is widespread in granulite terrains. Notable occurrences include parts of southern India, the Canadian Shield, Greenland, West Africa, and other ancient cratonic regions. The rocks are commonly found within extensive metamorphic crustal blocks and contribute to understanding crustal evolution and high-temperature metamorphism.

Name and taxonomy: charnockite denotes a rock type defined by its mineral assemblage and metamorphic origin, rather than by igneous origin. The term originates from historical type localities described in the late 19th century.