Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Its chemical formula is . It is found in igneous and some metamorphic rocks as well as in stony and iron meteorites. Many references have formally abandoned this term, preferring to categorise this mineral as enstatite or ferrosilite. It forms a solid solution series with the minerals enstatite and ferrosilite, being a mid-way member between the two. Pure enstatite contains no iron, while pure ferrosilite contains no magnesium; hypersthene is the name given to the mineral when a significant amount of both elements are present. Enstatite is stable at atmospheric pressure, but ferrosilite is stable only at elevated pressure, decomposing into quartz and fayalite at atmospheric pressure unless stabilized by magnesium or other impurities.
Distinctly developed crystals are rare, the mineral being usually found as foliated masses embedded in the igneous rocks norite and hypersthene-andesite, of which it forms an essential constituent.
Hypersthene has been discredited by the International Mineralogical Association and is no longer considered a valid mineral type; specimens labelled as hypersthere are usually ferroan enstatite.
References
- Mineral galleries
- Webmineral
- Mindat locations
- Enstatite-Hypersthene-Ferrosillite series