monchiquite


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monchiquite

[′man·chə‚kwīt]
(petrology)
A lamprophyre composed of olivine, pyroxene, and usually mica or amphibole phenocrysts embedded in a glass or analcime groundmass.
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Orthoclase occurs with microcline in Proterozoic rocks of the district, as phenocrysts in plagioclase phonolite, as a major constituent of tephriphonolite and vogesite, as a part of the ground-mass in monchiquite and as transparent to translucent crystals ("adularia") in both the veins and the inner and outer parts of altered host rocks (replacing biotite and microcline) of vein and diatreme-hosted deposits.
Pargasite is very common as brown to olive-green microphenocrysts in vogesite, as tan megacrysts in monchiquite, and in tephriphonolite and plagioclase phonolite (Birmingham, 1987).
Phlogopite occurs as phenocrysts and as a constituent of the groundmass in vogesite and monchiquite (Birmingham, 1987; Thompson, 1992).
In vogesite its composition ranges from andesine to bytownite, and minor albite occurs in the groundmass of monchiquite (Lindgren and Ransome, 1906; Loughlin and Koschmann, 1935; Thompson, 1992).