perthite


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perthite

[′pər‚thīt]
(geology)
A parallel to subparallel intergrowth of potassium and sodium feldspar; the potassium-rich phase is usually the host from which the sodium-rich phase evolves.
References in periodicals archive ?
The latter together with microcline, quartz (8-10%) and plagioclase (1-2%) constitutes the matrix to the megacrysts/phenocrysts that almost totally consist of perthite. Amphibole, biotite, opaque ore mineral, sphene, epidote, and aegirine augite are the commonly occurring mafic minerals, which collectively constitute about 25% by volume of the rock.
The rhyolite sheets are sparsely porphyritic, at places banded, and composed of perthite, quartz, albite, sodic amphibole, aegirine-augite, opaque oxide and titanite.
The rhyolite sheets are banded, sparsely porphyritic, and composed of perthite, quartz, albite, sodic amphibole, aegirine-augite, opaque oxide and titanite.
Rischorrite: A variety of nepheline syenite in which nepheline is poikilitically enclosed in microcline perthite. ("Poikilitic" refers to a texture in which small crystals of one mineral are irregularly scattered within a larger anhedral crystal of another mineral.) The name, given by Kupletsky in 1932, is for Rischorr in the Khibina complex, Kola Peninsula, Russia.
The granite is composed of perthite quartz some plagioclase opaque oxide biotite and/or amphibole and titanite whereas the quartz monzonite comprises perthite calcic oligoclase/andesine quartz and minor amount of mafic minerals similar to those of the granite.
Alkali feldspar laths up to 4 mm in length with patch perthite texture (Fig.
Detrital components include quartz feldspar (plagioclase orthoclase microcline and perthite) muscovite biotite and chlorite.
It consists of perthite, quartz, biotite, magnetite and epidote as the major constituents while amphibole, sphene, muscovite and zircon occur as accessories.
Beryl at Alto Ligonha occurs mainly in the perthite intermediate zone, in crystals up to 900 kg, and also near the quartz core (Sinkankas, 1988).
Dark grey Sadurous rhyolite is homogeneous and apparently banded, porphyritic to subporphyritic and fine grained mainly composed of K-feldspar (mainly perthite) and quartz with small amount of plagioclase.
The central part of the zoned pegmatite, where open-pit mining once exploited beryl, is composed essentially of giant-size perthite masses containing numerous books of pale muscovite, an irregular framework of quartz, several elongated and fluted masses of industrial-grade beryl, large laths of white weathered spodumene to more than 2 meters in length, and (branching) vein-like masses of triphylite to several tons in weight.