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For E-type chondrites, see Enstatite chondrite.
Category Inosilicate
(repeating unit)
Strunz classification 9.DA.05
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
Space group Pbca
Unit cell a = 18.23, b = 8.84
c = 5.19 [Å]; Z = 8
Color White, grey, green, yellow or brown - colorless in thin section.
Crystal habit Prismatic crystals, commonly lamellar, fibrous, or massive
Twinning Simple and lamellar on [100]
Cleavage Good/distinct on [210]
Fracture Uneven
Tenacity Brittle
Mohs scale hardness 5 to 6
Luster Vitreous, pearly on cleavage
Streak Gray
Diaphaneity Translucent to opaque
Specific gravity 3.2–3.3
Optical properties Biaxial (+)
Refractive index nα = 1.650–1.668; nβ = 1.652–1.673; nγ = 1.659–1.679
Birefringence δ = 0.009–0.011
Pleochroism Pale green to pale orange
2V angle 55–90°
References [1][2][3]


Polymorphs and varieties[edit]

Gem quality enstatite from Myanmar (size: 2.4×1.0×0.8 cm)




Bronzite variety from Bare Hills, Baltimore County, Maryland, USA (size: 9.6×7.5×4.9 cm)



Enstatite and the other orthorhombic pyroxenes are distinguished from those of the monoclinic series by their optical characteristics, such as straight extinction, much weaker double refraction and stronger pleochroism. They also have a prismatic cleavage that is perfect in two directions at 90 degrees. Enstatite is white, gray, greenish, or brown in color; its hardness is 5–6 on the Mohs scale, and its specific gravity is 3.2–3.3.


Isolated crystals are rare, but orthopyroxene is an essential constituent of various types of igneous rocks and metamorphic rocks. Magnesian orthopyroxene occurs in plutonic rocks such as gabbro (norite) and diorite. It may form small idiomorphic phenocrysts and also groundmass grains in volcanic rocks such as basalt, andesite, and dacite.

Enstatite, close to En90Fs10 in composition, is an essential mineral in typical peridotite and pyroxenite of the Earth's mantle. Xenoliths 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 serpentines. 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 Kjörrestad, near Brevig in southern Norway.

Enstatite is a common mineral in meteorites. Crystals have been found in stony and iron meteorites, 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 chondrules, with an internal radiated structure.

Enstatite in Space[edit]

Enstatite is one of the few silicate minerals that have been observed in crystalline form outside the Solar System, particularly around evolved stars and Planetary Nebulae such as NGC 6302. Enstatite is thought to be one of the early stages for the formation of crystalline silicates in space and many correlations have been noted between the occurrence of the mineral and the structure of the object around which it has been observed.[citation needed]

Enstatite is thought to be a main component of the E-type asteroids;[4] in the Solar System, the main example are Hungaria asteroids.