Pyroxene (rock-forming inosilicate minerals)
Pyroxenes are a major group of single-chain inosilicate minerals common in igneous and metamorphic rocks, important for petrology, classification, and interpreting Earth and planetary processes.
Pyroxenes are a diverse family of rock-forming inosilicate minerals that share a characteristic single-chain structure of silica tetrahedra. Their general chemical formula is represented as XY(Si,Al)2O6, where X and Y stand for various metal cations such as calcium, magnesium, iron, sodium and aluminum. Substitution of aluminum for silicon occurs only to a limited degree in most pyroxenes, distinguishing them from some other silicates.
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Structure and physical properties
The single chains of SiO4 tetrahedra give pyroxenes two nearly perfect cleavage directions at close to right angles, a diagnostic feature in hand specimens. Members range from nearly pure magnesium or iron end‑members to calcium-rich varieties. Crystallographically they fall mainly into two groups: orthorhombic (orthopyroxenes) and monoclinic (clinopyroxenes). Color, density and minor element content vary with composition, and some pyroxenes form attractive, translucent crystals that are used as gemstones.
Classification and common minerals
- Orthopyroxenes: enstatite–ferrosilite series (Mg–Fe rich).
- Clinopyroxenes: diopside, hedenbergite, augite and jadeite (Ca or Na bearing).
- Crossover and aluminous pyroxenes occur at higher pressures and in metamorphic environments.
Occurrence and geological importance
Pyroxenes are abundant in mafic and ultramafic igneous rocks such as basalt, gabbro and peridotite, and they are common constituents of metamorphic rocks formed at high temperature. Whole‑rock and mineral chemistry of pyroxenes are widely used by geologists to infer the pressure, temperature and composition of the rock’s source. Pyroxene‑rich igneous rocks are called pyroxenites when pyroxene dominates the mineral assemblage.
Uses, examples and notable facts
Although not widely used as industrial minerals, pyroxenes are crucial in petrology and planetary science: they occur in mantle xenoliths, meteorites and lunar samples, helping to reconstruct planetary interiors and magmatic histories. Gems such as jadeite are members of the pyroxene group. For introductory reading on inosilicate geometry see inosilicate structure and for mineral data consult general references like mineral databases.
Further reading and resources
To explore pyroxene chemistry and phase relations, see specialized texts and articles (mineral chemistry, petrology). Field identification guides cover texture and cleavage (field methods). For information about pyroxenite and rock classification consult petrologic summaries (igneous rocks, metamorphic rocks). Additional educational materials are available from outreach and academic portals (teaching resources).
Questions and answers
Q: What are pyroxenes?
A: Pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks.
Q: What is the structure of pyroxenes?
A: Pyroxenes share a common structure consisting of single chains of silica crystals with the general formula XY(Si,Al)2O6, where X and Y represent metal ions.
Q: What is the general formula for pyroxenes?
A: The general formula for pyroxenes is XY(Si,Al)2O6, where X and Y represent metal ions.
Q: Can aluminium substitute for silicon in pyroxenes?
A: Aluminium can substitute for silicon in silicates such as feldspars and amphiboles, but the substitution occurs only to a limited extent in most pyroxenes.
Q: What is pyroxenite?
A: Pyroxenite is an igneous rock made up of minerals from the pyroxene group.
Q: Are pyroxenes only found in igneous rocks?
A: No, pyroxenes are found in both igneous and metamorphic rocks.
Q: What is the chemical makeup of pyroxene?
A: The chemical makeup of pyroxene is XY(Si,Al)2O6, where X and Y represent metal ions.
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Author
AlegsaOnline.com Pyroxene (rock-forming inosilicate minerals) Leandro Alegsa
URL: https://en.alegsaonline.com/art/80249