Topic Page: Peridotite

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Topic Page: Peridotite Definition: peridotite from The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide Rock consisting largely of the mineral olivine; pyroxene and other minerals may

1 Topic Page: Peridotite Definition: peridotite from The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide Rock consisting largely of the mineral olivine; pyroxene and other minerals may also be present. Peridotite is an ultramafic rock containing less than 45% silica by weight. It is believed to be one of the rock types making up the Earth's upper mantle, and is sometimes brought from the depths to the surface by major movements, or as inclusions in lavas. Summary Article: Peridotite from Rock and Gem ONE OF THE MOST ECONOMICALLY important rocks, peridotite is the ultimate source of all chromium ore, and its variety kimberlite is the source of all naturally occurring diamonds. Fresh peridotite contains olivine, pyroxene, and chromite. Peridotite that has been altered by weathering becomes serpentinite, containing chrysotile, other serpentines, and talc. Formerly, peridotite was a major source of Image from: Poikilitic magnesite, an important economic mineral. It is also the major source of texture showing the small chrysotile asbestos, now of declining economic importance. crystals... in Guide to Minerals, Rocks and Fossils An intrusive igneous rock, peridotite is coarse-grained, dark-colored, and dense. It contains at least 40 per cent olivine. It is related to the rock pyroxenite in that they form in similar environments and both are olivine-pyroxene rocks. Pyroxenite contains at least 60 per cent pyroxene. Another related rock is dunite, a yellowish-green, intrusive igneous rock composed almost entirely of olivine. Like peridotite, dunite is an important source of the chromium ore chromite. Peridotite is found interlayered with iron- and magnesia-rich rocks in the lower parts of layered, igneous rock bodies, where its denser crystals formed first through selective crystallization and then settled to the bottom of still-fluid or semi-solid crystallizing mushes. Within peridotite bodies, layers of chromite (the principal ore of chromium), an early crystallite and the first to settle, can reach several yards thick. Peridotite is also found in mountain belts as irregular, olivine-rich masses, sometimes with related gabbro, and in dikes (vertical or steeply inclined sheet-like bodies, which often cut existing rock structure). Garnet is often present as an accessory mineral, and weathered peridotites are commonly a source of nickel. Peridotite s other important occurrence is in volcanic pipes as kimberlite. Properties Rock type Ultramafic, plutonic, igneous Major minerals Olivine, pyroxene Minor minerals Garnet, chromite Color Dark green to black Texture Coarse Green peridotite

2 This specimen from Lanzarote in the Canary Islands takes its green coloring from the mineral olivine present within it.

3 Exposed peridotite Gros Morne National Park in Newfoundland, Canada contains peridotite rocks from the Earth s mantle. Related rocks Both pyroxene and dunite are related to peridotite. They are deep-seated in origin, and contain a large proportion of olivine.

4 Dunite

Pyroxenite The Ear th s mantle Peridotite is a major structural component of the Earth. It is the major component of the asthenosphere, the upper portion of the mantle upon which the plates rest.

5 Pyroxenite The Ear th s mantle Peridotite is a major structural component of the Earth. It is the major component of the asthenosphere, the upper portion of the mantle upon which the plates rest. At depths of miles (70 200km), the mantle rocks are thought to exist at temperatures slightly above their melting point, and a small percentage may be molten. This gives the mantle the plasticity for continental movement. The basaltic

extent by the mineral make-up of the peridotite.

6 magmas of the oceanic crust are generated in the asthenosphere, their compositions determined to an extent by the mineral make-up of the peridotite. Lava flow The deepest magmas originate in the upper layer of the mantle.

7 M antle xenolith Fragments of mantle peridotite are brought to the surface by deep-seated magmas Dorling Kindersley Limited

8 APA Peridotite. (2008). In R. L. Bonewitz, Rock and gem (2nd ed.). London, UK: Dorling Kindersley Publishing, Inc. Retrieved from Chicago "Peridotite." In Rock and Gem, by Ronald L. Bonewitz. 2nd ed. Dorling Kindersley Publishing, Inc., Harvard Peridotite. (2008). In R.L. Bonewitz, Rock and gem. (2nd ed.). [Online]. London: Dorling Kindersley Publishing, Inc. Available from: [Accessed 8 April 2018]. MLA "Peridotite." Rock and Gem, Ronald L. Bonewitz, Dorling Kindersley Publishing, Inc., 2nd edition, Credo Reference,. Accessed 08 Apr

Name Class Date STUDY GUIDE FOR CONTENT MASTERY

Name Class Date STUDY GUIDE FOR CONTENT MASTERY Igneous Rocks What are igneous rocks? In your textbook, read about the nature of igneous rocks. Use each of the terms below just once to complete the following statements. extrusive igneous rock intrusive