The minerals enstatite and hypersthene

	Chemical Formula	Enstatite - Mg₂Si₂O₆ Hypersthene - (Mg,Fe)₂Si₂O₆
	Composition	Enstatite is magnesium silicate. However, it is usually contains some iron replacing some magnesium. When a significant amount of iron present, the mineral is called Hypersthene (magnesium iron silicate). [Most authorities agree that Hypersthene contains a ratio of magnesium to iron about 1:1. If only a small amount of iron is present, the mineral is still Enstatite.] In many reference guides, Hypersthene is categorized as a variety of Enstatite, and not as a separate mineral. Enstatite forms a series with Ferrosillite (FeSi₂O₆), in which the intermediary member is Hypersthene. Specimens of pure Enstatite (without any iron) are not common, and specimens of pure Ferrosillite (without any magnesium) are virtually unknown.
	Variable Formula	(Mg,Fe)Si₂O₆
	Color	Gray, green, dark yellow, yellow-brown, greenish-brown, brown, black
	Streak	Light brown to grayish-white
	Hardness	5 - 6
	Crystal Forms and Aggregates	(Orthorhombic) Usually as disordered aggregates of rectangular crystals. May also occur in single crystals (prismatic and stubby), which may be well-terminated. Also occurs as cleavage fragments, as platy groupings, fibrous, and lammelar. Crystals are partially hollow in some localities.
	Transparency	Transparent to opaque
	Specific Gravity	3.1 - 3.9 (The greater the iron content, the heavier it is)
	Luster	Vitreous, silky, submetallic, dull
	Cleavage	1,2 - prismatic at cleavage angles of 87º and 93º (characteristic of minerals in the pyroxene group). May also exhibit parting in one direction.
	Fracture	Uneven
	Tenacity	Brittle
	Other Names	Hypersthene can have three connotations. Most often, it refers to an individual mineral, which is midway in the Enstatite-Ferrosillite series. The term may also be used as an iron-rich variety of Enstatite, and it is occasionally used as a synonym for Enstatite and Ferrosillite. A synonym for Hypersthene is "Ferroan Enstatite".
	Varieties	Bronzite - Dark brown or greenish-brown, opaque variety with a submetallic luster. Chrome-enstatite - Emerald-green, chromium-rich variety
	Polymorphs	Polymorph of Enstatite is Clinoenstatite Polymorph of Hypersthene is Clinohypersthene
	In Group	Silicates ; Inosilicates ; Pyroxene group
	All About	Enstatite and Hypersthene are found in igneous environments, and are sometimes found in meteorites. Pure Enstatite is transparent and lightly colored; iron makes it darker and opaque.
	Uses	The variety Bronzite is used as a minor gemstone. It often contains inclusions of highly reflective minerals, such as Hematite and Goethite, which give it a bronze-like effect when polished (hence its name). Some polished specimens exhibit asterism or cat's eye effect.
	Striking Features	Luster and cleavage angles
	Popularity (1-4)	2
	Prevalence (1-3)	1
	Demand (1-3)	2
	Distinguishing Similar Minerals	Hornblende - different cleavage angles (otherwise difficult to distinguish) Augite - very difficult to distinguish Diopside - very difficult to distinguish
	Commonly Occurs With	Biotite, Almandine, Quartz, Diopside, Labradorite, Magnetite, Chromite, Serpentine (In meteorites, it occurs with Iron-nickel, Olivine, and Ferrosillite, as well as the high temperature polymorphs [ Clinoenstatite, Clinohypersthene, and Clinoferosillite ] )
	Noteworthy Localities	Enstatite is relatively abundant, and localities are worldwide. However, a few notable occurrences are the Tilly Foster Mine, Brewster, Putnam Co., New York; the Wood's Mine, near Texas, Lancaster Co., Pennsylvania; the Bare Hills, near Baltimore, Maryland; Jackson Co., North Carolina; and Boulder Co., Colorado. Hypersthene is much rarer than Enstatite. The most important deposit is in the Adirondack Mountains of New York (especially at Gore Mountain, Warren Co.). Small amounts were also found in Labrador, Canada, together with Labradorite. Hypersthene is also found in Brusand, Norway. Gem quality Bronzite is found in Styria, Austria; the Bushfield Complex, Transvaal, South Africa; and in the Stillwater Complex, Montana.
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