pyroxén

Pyroxene is a group of important rock-forming silicate minerals. They are characterized by a single chain (inosilicate) structure. The general formula for pyroxenes is XY(Si,Al)2O6, where X and Y are cations that can occupy different crystallographic sites. Commonly, X is a larger cation such as calcium, sodium, magnesium, or iron, and Y is a smaller cation like magnesium, iron, aluminum, or chromium. The silicon can sometimes be partially substituted by aluminum.

Pyroxenes are typically found in both igneous and metamorphic rocks. In igneous rocks, they are common constituents of mafic and ultramafic magmas, such as basalts and gabbros. They crystallize at relatively high temperatures and pressures. In metamorphic rocks, pyroxenes form under conditions of high temperature and pressure, often during regional metamorphism or contact metamorphism.

The appearance of pyroxenes varies widely depending on their specific composition. They can be black, brown, green, or even colorless. They often exhibit prismatic cleavage, breaking along planes that are roughly at right angles to each other. Common examples of pyroxenes include augite, enstatite, and diopside. Their presence and composition can provide valuable clues about the geological conditions under which the rocks they occur in were formed.