Peridotite

peridotite (pĕr'ēdō`tīt): see olivine.

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peridotite

Coarse-grained, heavy, igneous rock that contains at least 10% olivine, other iron- and magnesium-rich minerals (generally pyroxenes), and not more than 10% feldspar. Peridotite is the ultimate source of all chromium ore and naturally occurring diamonds, and of nearly all chrysotile asbestos. Nearly all peridotite is more or less altered to serpentine; in warm, humid climates peridotite and serpentine have weathered to soils and related deposits that, though now worked on a relatively small scale, are potential sources of iron, nickel, cobalt, and chromium.

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peridotite [pə′rid·ə‚tīt]

(petrology)

A dark-colored, ultrabasic phaneritic igneous rock composed largely of olivine, with smaller amounts of pyroxene or hornblende.

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Peridotite 

an ultrabasic intrusive rock that is chiefly composed of olivine and pyroxene and sometimes contains hornblende. The olivine and pyroxene contents range from 70 to 30 percent and 30 to 70 percent, respectively; peridotite also contains 40 to 46 percent SiO₂ and 34 to 46 percent MgO. Among the accessory minerals found in peridotite are magnetite, ilmen-ite, pyrrhotite, chromite, spinel, and garnet. In addition, peridotite sometimes contains platinum and certain nickel minerals.

Peridotite’s color is dark, usually green or greenish gray. When it is highly serpentinized with olivine and pyroxenes, it alters to serpentinite. Peridotite in combination with orthorhombic pyroxene is called saxonite, or harzburgite; with monoclinic pyroxene, wehrlite; and with both rhombic and monoclinic pyroxene, websterite, or lhertzolite. Peridotite in association with other ultrabasic and with basic rocks forms extensive belts and zones that are characterized by deposits of commercial minerals, including chromite, platinum ores, silicate nickel ores, chrysotile asbestos, and talc.