Pyroxenite

pyroxenite

Dark medium- to coarse-grained igneous rock that consists chiefly of pyroxene. Accessory minerals include hornblende, biotite, or olivine. Pyroxenites are not abundant.

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pyroxenite [pə′räk·sə‚nīt]

(petrology)

A heavy, dark-colored, phaneritic igneous rock composed largely of pyroxene with smaller amounts of olivine and hornblende, and formed by crystallization of gabbroic magma.

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Pyroxenite 

an ultrabasic rock composed chiefly of one or more pyroxenes. It sometimes contains small admixtures of olivine; more rarely, it contains feldspar and magnetite or titanomagnetite. The type of pyroxene and the ore minerals present in the rock form the basis for determination of the variety of pyroxenite. Thus, rocks containing bronzite are called bronzitites, while those with hypersthene are known as hypersthenites. Pyroxenites containing equal amounts of orthopyroxene and diopside are called websterites. Pyroxenites are composed of 43–53 percent SiO₂, 4–10 percent AI₂O₃, 5–13 percent FeO + F₂O₃, 13–24 percent MgO, and 9–20 percent CaO.

Pyroxenites are found in areas of basic plutons, forming rather extensive belts and zones. They are often associated with alkali rocks and carbonatites, thus producing deposits of many minerals, such as apatite and rare earths. Pyroxenites sometimes occur as titanium-rich iron ores.