Description
The pyroxenes (inosilicates) enstatite (chemical formula MgSiO3) and ferrosilite (Fe2+MgSiO3) form a complete solid solution series and are common rock-forming minerals in igneous and metamorphic rocks, and also in meteorites. The intermediate composition, with magnesium and iron2+, (Mg,Fe)SiO3, is also known as hypersthene, but this name is no longer officially used and has been replaced by enstatite or ferrosilite. Enstatite and the other orthorhombic pyroxenes differ from the monoclinic ones in their optical properties, such as quenching and pleochroism. The crystals have a distinct cleavage along the [110] and [010] crystal planes. Enstatite is white, gray, greenish, or brown. Its hardness is 5.5 and its density is 3.2 kg/dm3. The name of the mineral enstatite is derived from the Greek enstates, meaning "opponent" or "counterpart." It is so named because it forms the magnesium-bearing end member of the ferrosilite series. The bronze-brown variety of enstatite is called bronzite. Enstatite crystals are found in stony and iron meteorites, such as in the meteorite that fell near Breitenhach in the Ore Mountains, Bohemia. Large crystals, up to 30 centimeters long, are found in apatite veins intersecting mica schist at the Kjorrestad apatite mine, near Brevig in southern Norway. Individual crystals are rarely found because the mineral occurs in igneous or mantle rocks such as peridotite and pyroxenite. Weathering of these rocks forms the mineral serpentine. Small crystals are found in effusive rocks such as trachytes and andesites. The type locality of enstatite has not been further defined.
Bronzite
