peridotite

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peridotite

(pĕr'ēdō`tīt): see olivineolivine
, an iron-magnesium silicate mineral, (Mg,Fe)2SiO4, crystallizing in the orthorhombic system. It is a common constituent of magnesium-rich, silica-poor igneous rocks; metamorphism of some high magnesium sediments also can form olivine.
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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.

peridotite

[pə′rid·ə‚tīt]
(petrology)
A dark-colored, ultrabasic phaneritic igneous rock composed largely of olivine, with smaller amounts of pyroxene or hornblende.
References in periodicals archive ?
In summary, this kimberlite sampled a depleted peridotitic source which may also indicate higher diamond contents.
plus a further 7 Purple to Red peridotitic garnets (G9/ 10 Cr-pyrope)
Of the diamond indicator minerals found so far, numerous peridotitic G10 garnets and Group 1 eclogitic garnets have been recovered, together with significant amounts of chrome diopsides and olivines, all with diamond inclusion compositions.
The drilling program will also include several targets outside of the Nxau Nxau cluster; one in the Gcwihaba licences where a sodium-rich eclogitic (diamond inclusion) garnet was found in a loam sample over an airborne magnetic anomaly; and, one hole into each of three G9 peridotitic kimberlitic garnet anomalies over magnetic features in the Guma area (three out of four of these results were fully reported in our press release dated Wednesday, August 4, 2004).
The Mn content in most of the garnets is extremely depleted and also indicates a peridotitic diamond paragenesis.
It produced a significant number of peridotitic and eclogitic garnets, as well as some olivine and picroilmenite grains.
The mineralization occurs within a peridotitic border phase of an ultramafic intrusion.
Indicator minerals derived from kimberlite and till samples contain high interest peridotitic and eclogitic minerals, indicating that these kimberlites have potentially sampled both peridotitic and eclogitic diamonds.
Garnets of both eclogitic and peridotitic paragenesis have been recovered, however, G-9 type chrome pyropes are the most common indicator minerals present.
Indicator minerals such as chromite, eclogitic pyrope garnets and peridotitic pyrope garnets have been positively identified in core samples.
Angular and unabraided eclogitic and peridotitic garnets in the diamond stability field (indicating a local source) have been recovered in the area of geophysical anomalies identified from an airborne survey.