Picrite

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picrite

[′pi‚krīt]
(petrology)
A medium- to fine-grained igneous rock composed chiefly of olivine, with smaller amounts of pyroxene, hornblende, and plagioclase felspar.

Picrite

 

an effusive rock composed of augite and olivine. Pi-crite also contains admixtures of hornblende, biotite, and or-thopyroxene and of various secondary minerals, including ilmenite, magnetite, and apatite. The olivine is often altered and replaced by serpentine, as well as by iddingsite, chlorite, and sometimes actinolite.

Picrites are holocrystalline. However, they sometimes contain a certain amount of glass inset with augite and olivine (picrite porphyry). The chemical composition of picrites is 38–41 percent SiO2, 5-10 percent Al2O3, and 20-29 percent MgO.

References in periodicals archive ?
The picritic sills at Site 856 are the youngest magmas recovered from this segment of the ridge and display some of the most primitive compositions reported for the Juan de Fuca Ridge, suggesting that they postdate the existence of any robust magma chamber at Middle Valley (Stakes and Franklin 1994).
Primitive mantle-normalized incompatible-element patterns show remarkable depletion in the light REE, much like picritic sills at ODP Site 856, and are well below levels seen elsewhere on the northern Juan de Fuca Ridge (Leybourne and Van Wagoner 1991).
Volcanics are aphyric pillow basalts, picritic basalts and breccias made of volcanic and sedimentary clasts.
Primitive picritic tuff (high MgO, Cr; Mg# 62-81) must have been emplaced following rapid ascent, with minimal fractionation or crustal assimilation.
Kerr, A.C., and Arndt, N.T., 2001, A note on the IUGS reclassification of the high-Mg and picritic volcanic rocks: Journal of Petrology, v.
Ultramafic (picritic) rocks north of the Widgiemooltha Dome (Fig.
Melt, fluid and crystal inclusions in olivine phenocrysts from Kerguelen plume-derived picritic basalts; evidence for interaction with the Kerguelen Plateau lithosphere: Chemical Geology, v.