Enstatite

Enstatite is a magnesium silicate mineral with the chemical formula MgSiO3. It is a member of the pyroxene group and represents the magnesium end-member of the orthorhombic pyroxene series, in solid solution with ferrosilite (FeSiO3). It crystallizes in the orthorhombic system and commonly forms slender prismatic crystals. In hand specimens it is typically greenish to brownish, with a vitreous luster; in thin section it shows the characteristic two cleavages at near 90 degrees and moderate to high relief.

Enstatite occurs in a wide range of rocks, especially ultramafic and mafic rocks such as peridotite, dunite, basalt, and gabbro, and is a common constituent of meteorites, particularly enstatite chondrites. It forms at high temperatures in magnesium-rich magmas and is commonly associated with olivine, augite, and diopside. In meteorites, enstatite can occur in both the orthorhombic form and the monoclinic polymorph clinoenstatite, which forms under different pressure–temperature conditions.

The enstatite–ferrosilite solid solution reflects varying Fe/Mg content; rocks often contain mixtures of Mg- and Fe-rich pyroxenes. Enstatite is a primary rock-forming mineral and is used to interpret thermal history and oxidation conditions in planetary crusts and mantles, as well as in meteorite studies. It has no significant industrial uses but is important for petrological interpretation.