enstatit

Enstatit, or enstatite, is a magnesium silicate mineral with the chemical formula MgSiO3. It is the magnesium end-member of the orthopyroxene group within the pyroxene family and forms a complete solid-solution series with ferrosilite (FeSiO3). Enstatite commonly occurs in igneous and metamorphic rocks, particularly in ultramafic and mafic rocks such as peridotites, pyroxenites, and basalts, and can be a major constituent in mantle-derived rocks. It is also found in certain high-temperature metamorphic rocks and in primitive meteorites.

Crystallographically, enstatite belongs to the orthorhombic crystal system. It typically forms elongated prismatic crystals, but is often present as grains or masses in rocks. Physical properties include a Mohs hardness of 5–6, a vitreous to resinous luster, and a specific gravity around 3.2–3.3. It displays two directions of cleavage at approximately 87° and 93°, and has a color range from colorless to pale green, brown, or gray, depending on impurities.

In geology, enstatite is important for understanding mantle composition and the conditions of high-temperature metamorphism, as its presence, together with ferrosilite, reflects temperature, pressure, and oxygen fugacity. It also occurs in meteorites, notably enstatite chondrites and related asteroid-derived rocks, which provide insights into early solar system processes. Although enstatite can be cut and polished as a gemstone in rare cases, its use in jewelry is limited due to availability and color diversity. The mineral is named from Greek roots related to its character in pyroxene assemblages.