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Enstatite is a mineral; the magnesium endmember of the pyroxene silicate mineral series enstatite (MgSiO3) – ferrosilite (FeSiO3). The magnesium rich members of the solid solution series are common rock-forming found in igneous and metamorphic rock rocks. The intermediate composition, , has historically been known as hypersthene, although this name has been formally abandoned and replaced by orthopyroxene. When determined Petrography or chemically the composition is given as relative proportions of enstatite (En) and ferrosilite (Fs) (e.g., En80Fs20).
Weathering enstatite with a small amount of iron takes on a submetallic luster and a bronze-like color. This material is termed bronzite, although it is more correctly called altered enstatite.
Bronzite and hypersthene were known long before enstatite, which was first described by G. A. Kenngott in 1855. An emerald-green variety of enstatite is called chrome-enstatite and is cut as a gemstone. The green color is caused by traces of chromium, hence the varietal name. In addition, black, chatoyant hypersthene and brownish bronzite are also used as semi-precious gemstones.
Enstatite, close to En90Fs10 in composition, is an essential mineral in typical peridotite and pyroxenite of the Earth's mantle. of peridotite are common in kimberlite and in some basalt. Measurements of the calcium, aluminum, and chromium contents of enstatite in these xenoliths have been crucial in reconstructing the depths from which the xenoliths were plucked by the ascending magmas.
Orthopyroxene is an important constituent of some metamorphic rocks such as granulite. Orthopyroxene near pure enstatite in composition occurs in some metamorphosed serpentine group. Large crystals, a foot in length and mostly altered to steatite, were found in 1874 in the apatite veins traversing mica-schist and hornblende-schist at the apatite mine of Kjørstad, near Brevik in southern Norway.
Enstatite is a common mineral in meteorites. have been found in stony and iron , including one that fell at Breitenbach in the Ore Mountains, Bohemia. In some meteorites, together with olivine it forms the bulk of the material; it can occur in small spherical masses, or , with an internal radiated structure.
Enstatite is thought to be a main component of the . H. U. Keller, et al. - E-Type Asteroid (2867) Steins as Imaged by OSIRIS on Board Rosetta - Science 8 January 2010: Vol. 327. no. 5962, pp. 190 - 193 The Hungaria asteroids are the main examples in the Solar System.
A layer of quartz and enstatite clouds above an iron cloud deck are thought to exist in the atmosphere of the young brown dwarf 2M2224-0158.
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