Pyroxenes are a group of silicate minerals that are essential constituents of many igneous rocks, particularly those derived from the Earth's mantle. They are also found in some metamorphic rocks. Pyroxenes have a general formula of XY(Si,Al)2O6, where X represents calcium (Ca), sodium (Na), iron (Fe2+), or magnesium (Mg) and Y can be chromium (Cr), aluminium (Al), iron (Fe2+), magnesium (Mg), manganese (Mn), scandium (Sc), titanium (Ti), vanadium (V), or iron (Fe3+).
The structure of pyroxenes is characterized by a single chain of silica tetrahedra, which gives them a prismatic habit. This chain structure makes them part of the inosilicates group. Their crystal structure often displays a monoclinic symmetry, although some pyroxenes can also be orthorhombic.
The name "pyroxene" comes from the Greek words for "fire" (pyr) and "stranger" (xenos), alluding to the fact that some pyroxenes were found in the slag of furnaces, where they did not melt like other minerals. Pyroxenes were first described in the late 18th century, with detailed studies beginning in the 19th century as part of the broader classification of rock-forming minerals.
Pyroxenes are significant in geology because they: