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The Collaborative International Dictionary

Peridotite \Per"i*do*tite\, n. [Cf. F. p['e]ridotite.] (Min.) An eruptive rock characterized by the presence of chrysolite (peridot). It also usually contains pyroxene, enstatite, chromite, etc. It is often altered to serpentine.

Note: The chief diamond deposits in South Africa occur in a more or less altered peridotite.


n. (context geology English) A rock consisting of small crystals of olivine, pyroxene and hornblende; the major constituent of the Earth's mantle.


n. a dark coarse-grained igneous rock consisting principally of olivine


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, 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 pyroxenes, chromite, plagioclase, and amphibole.

Peridotite is the dominant rock of the upper part of the Earth's mantle. The compositions of peridotite nodules found in certain basalts and diamond pipes ( kimberlites) are of special interest, because they provide samples of the Earth's mantle brought up from depths ranging from about 30 km to 200 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 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. 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.

Usage examples of "peridotite".

Like enstatite, bronzite is a constituent of many basic igneous rocks, such as norites, gabbros, and especially peridotites, and of the serpentines which have been derived from them.

We know that to a depth of about a hundred miles the mantle consists predominantly of a type of rock known as peridotite, but what fills the space beyond is uncertain.

After three days the side effects of some of the component minerals, primarily peridotite and olivine, cause violent mental aberrations and hallucinations.

Back of the gold-bearing quartz lies an enormous deposit of altered peridotite, which contains diamonds, in the search for which it evidently became necessary to extend one of the shafts to the opposite side of the mountain, possibly for purposes of ventilation.

They consisted of a mixture of iron, nickel, peridotite, magnesium, and silicates.

One of them was a small block of peridotite, polished smooth before a single diagonal was cut across its coarse crystals.