Enstatite

Enstatite
General
Category	Inosilicate
Formula (repeating unit)	MgSiO3
IMA symbol	En[1]
Strunz classification	9.DA.05
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pbca
Unit cell	a = 18.23, b = 8.84 c = 5.19 [Å]; Z = 8
Identification
Formula mass	100.387 g·mol−1
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	Pink to green pleochroism diagnostic for enstatite, pale green to pale orange perpendicular to pink-green axis
2V angle	55–90°
References	[2][3][4]

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 minerals found in igneous and metamorphic rocks. The intermediate composition, (Mg,Fe)SiO
₃, has historically been known as hypersthene, although this name has been formally abandoned and replaced by orthopyroxene. When determined petrographically or chemically the composition is given as relative proportions of enstatite (En) and ferrosilite (Fs) (e.g., En₈₀Fs₂₀).