hypersthene

Hypersthene is a historic mineral name used for a range of iron- and magnesium-rich orthorhombic pyroxenes in the pyroxene group. In older mineralogy it referred to the orthorhombic member of the enstatite–ferrosilite series with relatively high iron content. In modern nomenclature the term hypersthene is largely obsolete; minerals formerly labeled hypersthene are now described as orthopyroxenes with compositions along the enstatite (MgSiO3)–ferrosilite (FeSiO3) solid solution.

Occurrence and formation: Hypersthene occurs in igneous rocks from basaltic to andesitic compositions and in high-temperature metamorphic rocks such as granulites. It is common in ultramafic rocks like peridotite and pyroxenite and is often found together with olivine and other pyroxenes. Its presence reflects crystallization conditions with relatively high temperatures and varying iron-magnesium ratios.

Physical properties and structure: Hypersthene belongs to the orthorhombic pyroxene group. It typically displays two good cleavage planes at nearly 90 degrees and has a vitreous to submetallic luster. Color ranges from brown to dark brown or black, with a hardness around 5–6 on the Mohs scale. Its crystal structure and composition place it within the broader orthopyroxene family rather than as a separate mineral species.

Notes: In contemporary literature, the terms bronzite and hypersthene are used less often; rocks containing such compositions are described by their orthopyroxene content and the Mg–Fe ratio rather than as distinct mineral species.