Editing Pyroxenite (section)

==Intrusive and mantle pyroxenites==
[[File:Metapyroxenite from the Ophiolite on Unst in Shetland Islands in Scotland.jpg|thumb|Metamorphosed clinopyroxenite, made of green diopside, from the Shetland [[ophiolite]], [[Unst]], Scotland]]
Igneous pyroxenites are closely allied to [[gabbro]]s and [[norite]]s, from which they differ by the absence of [[feldspar]], and to [[peridotite]]s, which are distinguished from them by containing more than 40% [[olivine]]. This connection is indicated also by their mode of occurrence, for they usually accompany masses of gabbro and peridotite and seldom are found by themselves.

They are often very coarse-grained, containing individual [[crystal]]s which may be several inches in length. The principal accessory minerals, in addition to olivine and feldspar, are [[chromite]] and other [[spinel]]s, [[garnet]], [[magnetite]], [[rutile]], and [[scapolite]].

Pyroxenites can be formed as cumulates in [[Layered intrusion|ultramafic intrusions]] by accumulation of pyroxene crystals at the base of the magma chamber. Here they are generally associated with gabbro and anorthite cumulate layers and are typically high up in the intrusion. They may be accompanied by [[magnetite]] layers, [[ilmenite]] layers, but rarely [[chromite]] cumulates.

Pyroxenites are also found as layers within masses of peridotite. These layers most commonly have been interpreted as products of reaction between ascending magmas and peridotite of the [[upper mantle (Earth)|upper mantle]]. The layers typically are a few centimeters to a meter or so in thickness. Pyroxenites that occur as [[xenolith]]s in [[basalt]] and in [[kimberlite]] have been interpreted as fragments of such layers. Although some mantle pyroxenites contain garnet, they are not [[eclogite]]s, as clinopyroxene in them is less sodic than [[omphacite]] and the pyroxenite compositions typically are unlike that of [[basalt]]. Pyroxenites might play an important role in basalt genesis (e.g., Lambart et al., 2016), either by contributing directly to the magma production, or indirectly as the result of reaction between peridotite and magma derived from partial melting of eclogite (e.g., Sobolev and others, 2007).