Peridotite: Difference between revisions

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'''Peridotite''' is a dense, coarse-grained [[igneous rock]] consisting mostly of the 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 the [[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 part of the [[Mantle (geology)|Earth's mantle]]. The compositions of peridotite [[nodule (geology)|nodules]] found in certain basalts and [[kimberlite pipe|diamond pipes]] ([[kimberlite]]s) are of special interest, because they provide samples of the 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 the earth was formed, and so they are of special interest to [[paleogeology|paleogeologists]] because they provide clues to the early composition of the 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 in color; 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 such as blue, brown, and red.