is a common rock-forming inosilicate mineral
belonging to the group of orthorhombic pyroxenes
. Many references have formally abandoned this term, preferring to categorise this mineral as enstatite or ferrosilite
. It is found in igneous
and some metamorphic rocks
as well as in stony and iron meteorites
. 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 ferrosillite contains no magnesium; hypersthene is the name given to the mineral when a significant amount of both elements are present. The chemical formula is (Mg,Fe)SiO3
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. The coarse-grained labradorite-hypersthene-rock (norite) of the island of Paul off the coast of Labrador has furnished the most typical material; and for this reason the mineral has been known as Labrador hornblende or paulite.
Color is often gray, brown or green, and the luster is usually vitreous to pearly. The pleochroism is strong, the hardness is 5 - 6, and the specific gravity is 3.4 - 3.9. On certain surfaces it displays a brilliant copper-red metallic sheen, or schiller, which has the same origin as the bronzy sheen of bronzite, but is even more pronounced. Like bronzite, it is sometimes cut and polished as a gemstone.
The name hypersthene comes from the Greek and means "over strength". It is in allusion to its greater hardness than the amphibole mineral hornblende, a mineral with which it is often confused.