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Pyroxene

Any of a group of crystalline silicate minerals common in igneous and metamorphic rocks and containing two metallic oxides, as of magnesium, iron, calcium, sodium, or aluminum. The pyroxene mineral group is of particular interest in planetary sciences. Determining the compositional and structural characteristics of pyroxenes in rocks can be crucial to understanding their petrogenesis.

A large, geologically significant group of dark, rock-forming silicate minerals. Pyroxene is found in abundance in a wide variety of igneous and metamorphic rocks. Because of their structural complexity and their diversity of chemical composition and geologic occurrence, these minerals have been intensively studied by using a wide variety of modern analytical techniques. Knowledge of pyroxene compositions, crystal structures, phase relations, and detailed microstructures provides important information about the origin and thermal history of rocks in which they occur.

Pyroxene is one of the three main minerals that makes up basalt. The most common pyroxenes are magnesium, calcium, and iron silicates. A common pyroxene is augite which is very abundant in many igneous rocks such as basalt and gabbro. We often want to confuse pyroxene with amphibole because they are both mafic minerals found in mafic igneous rocks but the amphibole is shiny black and shows abundant parallel cleavages.

Pyroxenes are found in many rocks, often those crystallized from a melt (sometimes in metamorphic rocks). Pyroxene minerals are common in in meteorites and the extrusive igneous rock called basalt. There are many different types of pyroxene including augite, wollastonite, diopside, enstatite, and hypersthene. All of the types contain Si₂O₆ but some have sodium (Na) while others have iron (Fe), magnesium (Mg), or a combination of these three elements.

A group of important rock-forming silicate minerals of variable composition, among which calcium-, magnesium-, and iron-rich varieties predominate. Common pyroxenes belong to either the low-calcium enstatite-(ortho)ferrosilite series, (Mg,Fe)SiO₃, or the high-calcium diopside-hedenbergite series, Ca(Mg,Fe)Si₂O₆. Rare pyroxenes include jadeite, aegirine, and johannsenite.

See also: Enstatite.

Material Notes:
Silicates of lime, alumina, magnesia and iron (Augite).

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