Editing Peridotite (section)

{{Short description|Coarse-grained ultramafic igneous rock type}}

{{Infobox rock
|name = Peridotite
|type = Igneous
|image = Peridotite mantle xenoliths in phonotephrite (Peridot Mesa Flow, Middle Pleistocene, 580 ka; Peridot Mesa, San Carlos Volcanic Field, Arizona, USA) 28 (cropped)).jpg
|image_size = 300px
|caption = 
|composition = [[olivine]], [[pyroxene]]
}}

'''Peridotite''' ({{IPAc-en|US|ˈ|p|ɛ|r|ɪ|d|oʊ|ˌ|t|aɪ|t|,_|p|ə|ˈ|r|ɪ|d|ə|-}} {{respell|PERR|ih|doh|tyte|,_|pə|RID|ə|-}}) is a dense, coarse-grained [[igneous rock]] consisting mostly of the silicate minerals [[olivine]] and [[pyroxene]]. Peridotite is [[ultramafic]], as the rock contains less than 45% [[silica]]. It is high in [[magnesium]] (Mg<sup>2+</sup>), reflecting the high proportions of magnesium-rich olivine, with appreciable [[iron]]. Peridotite is derived from [[Earth's mantle]], either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle. The compositions of peridotites from these layered [[igneous]] complexes vary widely, reflecting the relative proportions of [[pyroxene]]s, [[chromite]], [[plagioclase]], and [[amphibole]].

Peridotite is the dominant rock of the [[upper mantle (Earth)|upper part of Earth's mantle]]. The compositions of peridotite [[nodule (geology)|nodules]] found in certain basalts are of special interest along with [[kimberlite pipe|diamond pipes]] ([[kimberlite]]), because they provide samples of Earth's mantle brought up from depths ranging from about 30&nbsp;km to 200&nbsp;km or more. Some of the nodules preserve [[isotope]] ratios of [[osmium]] and other elements that record processes that occurred when Earth was formed, and so they are of special interest to [[historical geology|paleogeologists]] because they provide clues to the early composition of Earth's mantle and the complexities of the processes that occurred.

The word ''peridotite'' comes from the gemstone [[peridot]], which consists of pale green olivine.<ref>Collins Australian Dictionary, 7th edition</ref> Classic peridotite is bright green with some specks of black, although most hand samples tend to be darker green. Peridotitic outcrops typically range from earthy bright yellow to dark green; this is because olivine is easily weathered to [[iddingsite]]. While green and yellow are the most common colors, peridotitic rocks may exhibit a wide range of colors including blue, brown, and red.