Piroxenos

Piroxenos, more commonly written as pyroxenes in English, are a group of inosilicate minerals that form single-chain silicate structures. They are among the most important rock-forming minerals in both the Earth’s crust and mantle, occurring in a wide range of igneous and metamorphic rocks. Pyroxenes typically exhibit two good cleavages at or near 90 degrees and vary in color from green and brown to black, with a vitreous to resinous luster. They can occur as orthopyroxenes, which crystallize in the orthorhombic system, or clinopyroxenes, which crystallize in the monoclinic system.

Chemically, pyroxenes have a general formula XY(Si,Al)2O6, where X and Y are cation sites that can host a variety of metal ions such as calcium, magnesium, iron, sodium, and aluminum. The composition forms extensive solid-solution series, yielding numerous end-members. Key orthopyroxene members include enstatite (MgSiO3) and ferrosilite (FeSiO3). Key clinopyroxene members include diopside (CaMgSi2O6), hedenbergite (CaFeSi2O6), and jadeite (NaAlSi2O6), with augite representing a broad Ca-Mg-Fe-Na-Al solid solution.

Occurrence and formation are controlled by temperature, pressure, and rock type. Pyroxenes are abundant in ultramafic and mafic igneous rocks such as peridotite, basalt, and gabbro, and they are common in metamorphic rocks formed under various conditions. They also occur in meteoritic material and certain high-temperature geological environments. Due to their stability and distinct compositional series, pyroxenes are frequently used in petrography and geothermobarometry to infer the history of rocks.