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The Mineral enstatite

Gemmy Enstatite Crystal

Enstatite forms series with the rare mineral Ferrosillite (Fe2Si2O6). Pure Enstatite (without any at all iron) is not common, and pure Ferrosillite (without any magnesium) is extremely rare. A common intermediary member of this series is known as Hypersthene, with a chemical formula of (Mg,Fe)2Si2O6. Although the term Hypersthene has been discredited by the IMA in 1998, it is still commonly used by many reference guides and is labeled as such in many collections.

Pure Enstatite is transparent and lightly colored; the iron content is responsible for the darker colors and increased opacity.

Chemical Formula

Mg2Si2O6

Color

Gray, green, dark yellow, yellow-brown, greenish-brown, brown, black

Crystal System

Orthorhombic

Properties

Streak
Light brown to grayish-white
Hardness
5 - 6
Transparency
Transparent to opaque
Specific Gravity
3.1 - 3.9
Luster
Vitreous, silky, 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

Crystal Habits

As disordered aggregates of rectangular crystals. May also occur in single prismatic and stubby crystals, which may be well-terminated. Also as cleavage fragments, as platy groupings, fibrous masses, radiating, and lammelar. Crystals are partially hollow or dissolved in some localities.

3D Crystal Atlas

Additional Information

Composition
Magnesium silicate, often with significant iron impurities.
In Group
Silicates; Inosilicates; Pyroxene Group
Striking Features
Luster and cleavage angles
Environment
As a rock-forming mineral in various igneous environment, and in metamorphosed Serpentine deposits. Also as a constituent of some meteorites.

Varieties

 -   Dark brown or greenish-brown, weathered variety of Enstatite with a high luster. It often contains impurities of Hematite and Goethite, which are responsible for its bronze-like color sheen.
 -   Deep forest-green, chromium-rich variety of Enstatite.
 -   Iron-rich variety of Enstatite, which was historically classified as an individual mineral species until 1998, when it was discredited by the IMA. The chemical form of Hypersthene is (Mg,Fe)2Si2O6.

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). Polished Bronzite may also exhibit asterism or cat's eye effect.

Noteworthy Localities

A classic Bronzite occurrence is the chrome mines of Kraubath, Styria, Austria. Small, transparent crystals come from Mont-Dore, Auvergne, France; and an exceptionally gemmy olive-green form comes from Mogok, Mynamar (Burma); and from the Kilosa District, Morogoro, Tanzania.

In the U.S., localities include the the Tilly Foster Mine, Brewster, Putnam Co., New York; Gore Mountain, Warren Co., New York; the Wood's Chrome Mine, Texas, Lancaster Co., Pennsylvania; Summit Rock, Klamath Co., Oregon; and Nain, Labrador, Canada. Good Bronzite comes from the Bare Hills, Baltimore Co., Maryland; and Webster, Jackson Co., North Carolina.

Distingushing Similar Minerals

Hornblende - Different cleavage angles (otherwise difficult to distinguish).
Diopside and Augite - Very difficult to distinguish.

enstatite Photos



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