pyroxen

Pyroxene is a group of inosilicate minerals that are among the most common rock-forming minerals in Earth's crust and mantle. They are single-chain silicates with the general formula XY(Si,Al)2O6, where X and Y are metal cations such as calcium, magnesium, iron, or sodium. SiO3 tetrahedra share two oxygens to form chains, which link to create the characteristic pyroxene structure. The two main structural subgroups are orthopyroxene and clinopyroxene.

Orthopyroxenes crystallize in the orthorhombic system and include enstatite (MgSiO3) and ferrosilite (FeSiO3) as end-members. Clinopyroxenes crystallize in the monoclinic system and include diopside (CaMgSi2O6) and hedenbergite (CaFeSi2O6), as well as a wide solid-solution with aluminum and sodium; augite is a common member of this group. Pyroxenes range in composition from magnesium- and iron-rich to calcium-rich varieties and often occur in solid-solution series.

Pyroxenes occur in a wide range of rocks, from ultramafic peridotites and pyroxenites to basalt, diabase, and gabbro, and they are also prominent in many high-temperature metamorphic rocks. They form by crystallization from mafic magmas or during metamorphism when rocks are subjected to high temperatures and pressures. Pyroxenes typically display two good cleavages intersecting at near 90 degrees, a vitreous to pearly luster, and colors that span green to brown to black in mafic varieties.

In petrology, pyroxenes are used to infer crystallization conditions and rock history. The compositional space of pyroxenes—often represented by the pyroxene quadrilateral (enstatite–ferrosilite–diopside–hedenbergite)—helps estimate temperature, pressure, and magmatic evolution in rocks.