Pyroxenite


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pyroxenite

[pə′räk·sə‚nīt]
(petrology)
A heavy, dark-colored, phaneritic igneous rock composed largely of pyroxene with smaller amounts of olivine and hornblende, and formed by crystallization of gabbroic magma.

Pyroxenite

 

an ultrabasic rock composed chiefly of one or more pyroxenes. It sometimes contains small admixtures of olivine; more rarely, it contains feldspar and magnetite or titanomagnetite. The type of pyroxene and the ore minerals present in the rock form the basis for determination of the variety of pyroxenite. Thus, rocks containing bronzite are called bronzitites, while those with hypersthene are known as hypersthenites. Pyroxenites containing equal amounts of orthopyroxene and diopside are called websterites. Pyroxenites are composed of 43–53 percent SiO2, 4–10 percent AI2O3, 5–13 percent FeO + F2O3, 13–24 percent MgO, and 9–20 percent CaO.

Pyroxenites are found in areas of basic plutons, forming rather extensive belts and zones. They are often associated with alkali rocks and carbonatites, thus producing deposits of many minerals, such as apatite and rare earths. Pyroxenites sometimes occur as titanium-rich iron ores.

References in periodicals archive ?
The ultramaphic rocks include Dunites, Harzburgites, lherzolites, Verlites and Pyroxenite that transform into Serpentine due to the erosion under certain climatic conditions and oxidation environment.
In the Hosenbein pluton, possible textural and structural indicators for the palaeo-porous flow of intercumulus melts include (1) mottled texture (2) pyroxenite aggregates, and (3) ferrodiorite dykes and patches.
These geophysical targets lie beneath glacial cover, however they are within a broad area of mapped mafic and ultramafic rocks where prospecting has identified local occurrences of nickel-copper sulphide mineralization associated with norite and pyroxenite intrusions.
These were reported to have intersected high-MgO serpentinized peridotite, pyroxenite and gabbro rocks, confirming the presence of prospective mafic-ultramafic rock types in the area.
The fluids changed the chemical composition and the environment of the rocks and resulted in mineral alterations, including the deposition of apatite in the pyroxenite.
The deposit comprises a central iron rich breccia (subsequently mined out), surrounded by a pyroxenite plug, into which carbonatite has intruded as a series of dykes and cone sheets.
Three of these locate on gabbro and pyroxenite, one of which is spatially associated with a copper in soil anomaly located within the keel of plunging syncline in gabbro.
Graham (1917) and Poitevin and Graham (1918) proposed that the rocks of the Serpentinite Zone were comagmatic, and described several gradual contacts between pyroxenite and gabbro at the Mill Hill section in the Asbestos igneous complex.
1), comprises gabbro, pyroxenite, and relatively homogeneous harzburgites (mantle tectonite?
confirmed March 8th/08 the presence of substantial PGE mineralization associated with chromite layers in pyroxenite unit.
The average Fe of 21% is typical for pyroxenite, and during operations a mining engineer will be testing the head grade to ensure it meets the cut off grade.
The base ultramafic layer, pyroxenite to serpentinite in composition, overlies the Chain Lakes massif (Fig.