Other meanings of Pyroxene
Mineralogy
Pyroxenes are a group of important rock-forming silicate minerals found in many igneous and metamorphic rocks. They share a common crystal structure of single chains of silica tetrahedra, with the general formula XYSi2O6, where X and Y are metal cations. Pyroxenes are essential constituents of the Earth's mantle and crust, and they also occur in meteorites and on other planetary bodies.
Pyroxenes are inosilicates characterized by single chains of silica tetrahedra (SiO4) linked by sharing two oxygen atoms, giving a Si:O ratio of 1:3. The chains are bonded laterally by cations in two distinct sites: the M1 site (octahedral, typically occupied by Mg, Fe2+, Al, or Ti) and the M2 site (larger, irregular, often Ca, Na, or Fe2+). This arrangement produces two cleavage planes intersecting at nearly 90°, a key diagnostic feature distinguishing pyroxenes from amphiboles, which cleave at about 124°.1
The general formula is XYSi2O6, where X and Y represent cations. Substitutions create a solid-solution series, notably the enstatite–ferrosilite series (orthopyroxenes) and the diopside–hedenbergite series (clinopyroxenes). The presence of calcium or sodium in the M2 site dictates the symmetry: orthopyroxenes are orthorhombic, while clinopyroxenes are monoclinic.2
Pyroxenes are among the most abundant minerals in the Earth's upper mantle, where they coexist with olivine and garnet in peridotites. They are also major components of basalts, gabbros, and andesites, and they crystallize from magmas over a wide temperature range. In metamorphic rocks, pyroxenes such as diopside and augite are typical of granulite facies and contact metamorphism of impure carbonates.3
Their composition records pressure–temperature conditions of formation, making them valuable geothermobarometers. For example, the jadeite content in clinopyroxenes is used to estimate depths of subduction. Pyroxenes also occur in meteorites, where they provide clues about early solar system processes, and in lunar basalts collected by Apollo missions.4
Beyond the common species, pyroxenes include rare varieties with unusual chemistries. Kosmochlor, a sodium-chromium clinopyroxene, is found in meteorites and in the jadeite-rich rocks of Myanmar. Pigeonite, a calcium-poor clinopyroxene, is a metastable phase that commonly appears in rapidly cooled volcanic rocks. Spodumene, a lithium pyroxene, is an important ore of lithium and can form gem-quality crystals, including the pink variety kunzite and the green hiddenite.5
Pyroxenes also exhibit exsolution textures, such as lamellae of augite in orthopyroxene, which result from slow cooling and are used to infer cooling rates. In planetary science, pyroxene spectra are used to map the mineralogy of Mars and the Moon from orbit, and the discovery of enstatite in cometary dust suggests that pyroxenes formed in the early solar nebula.6
The name "pyroxene" derives from the Greek words for "fire" and "stranger," coined by René Just Haüy in 1796 because he mistakenly thought the crystals were foreign to volcanic lavas. Pyroxenes have been used as gemstones (jadeite and spodumene) and as industrial minerals; for example, augite is used in ceramics and as a flux in glassmaking. Spodumene is a primary source of lithium, critical for batteries and electronics.7
In archaeology, pyroxene-bearing rocks such as jadeite were carved into tools and ornaments by ancient cultures, including the Olmec and Maori. The study of pyroxenes has also advanced experimental petrology, as they are used to calibrate high-pressure experiments that simulate mantle conditions.8
Pyroxenes are a diverse and widespread group of minerals, essential to understanding Earth's interior and planetary evolution.
Help improve the encyclopedia. Reports go straight to the site manager.