Pyroxene


The pyroxenes are a group of important rock-forming silicate minerals found in many igneous and metamorphic rocks. They share a common structure comprised of single chains of silica tetrahedra and they crystalise in the monoclinic and orthorhombic system. Pyroxenes have the general formula XY(Si,Al)<sub>2</sub>O<sub>6</sub> (where X represents calcium, sodium, iron<sup>+2</sup> and magnesium and more rarely zinc, manganese and lithium and Y represents ions of smaller size, such as chromium, aluminium, iron<sup>+3</sup>, magnesium, manganese, scandium, titanium, vanadium and even iron<sup>+2</sup>). Although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes.