Hypersthene

Hardness: 5-5.5 (Mohs), Color: Typically black, but can be dark brown, dark green, or gray. Often exhibits a metallic luster, sometimes with a bronze-like shimmer due to exsolution lamellae (schiller effect). Crystal structure: Orthorhombic. Cleavage: Good in two directions at nearly 90 degrees. Specific Gravity: 3.2-3.4.

Hypersthene forms in high-temperature igneous and metamorphic rocks. In igneous rocks, it crystallizes from magnesium-rich and silica-deficient magmas, found in mafic and ultramafic igneous rocks like norite, gabbro, and some basalts. In metamorphic rocks, it is a common mineral in high-grade metamorphic rocks such as granulites. Its formation is indicative of conditions involving high temperatures and pressures. Geological age varies depending on the host rock, ranging from ancient Precambrian to more recent volcanic formations.

Primarily a mineral of geological interest and a rock-forming mineral. When found in large, attractive crystals with a strong schiller effect, it is cut and polished into cabochons for jewelry. It has no significant industrial uses beyond its role in rock composition.

Hypersthene is part of the pyroxene group of minerals, specifically an orthopyroxene. Its name comes from the Greek words 'hyper' (above) and 'stenos' (strength), referring to its greater hardness when compared to hornblende, with which it was once confused. It is sometimes used as a minor gemstone, particularly varieties exhibiting a strong schiller effect, which makes them appear to glow internally.

In the field, hypersthene can be identified by its dark color, metallic or bronze-like luster (especially the schiller effect), moderate hardness, and its two distinct cleavages at nearly 90 degrees. It can be confused with other dark minerals like augite (which has monoclinic symmetry and different cleavage angles) or bronzite (which is an iron-poor hypersthene with a more pronounced bronze luster). It is commonly found in norites (which are igneous rocks), gabbros, granulites, and certain types of metamorphic gneisses. Notable localities include Labrador (Canada), Norway, Sweden, and parts of the USA.