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 rhyolite sheets are sparsely porphyritic, at places banded, and composed of perthite, quartz, albite, sodic amphibole, aegirine-augite, opaque oxide and titanite.
The rocks comprise plagioclase, perthite, quartz, and small amounts of biotite, opaque oxide, titanite, rare allanite, and secondary chlorite (after biotite), leucoxene and epidote.
The rhyolite sheets are banded, sparsely porphyritic, and composed of perthite, quartz, albite, sodic amphibole, aegirine-augite, opaque oxide and titanite.
Most rocks under the microscope are medium-grained hypidiomorphic to allotriomorphic subequigranular and composed of plagioclase hornblendic amphibole opaque iron oxide quartz and in some biotite titanite and rare perthite.
It is essentially composed of perthite and quartz with smaller to trace amounts of plagioclase biotite amphibole (not in all) opaque oxide titanite apatite and zircon.
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).
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.
Quartz, plagioclase, perthite and hornblende are the primary minerals while epidote, chlorite, biotite and muscovite are secondary minerals formed by alteration of feldspar and amphibole.
The pegmatite can be separated into two parts: (1) a northern near-vertical perthite dike which strikes N50-60 [degrees] E and (2) a southern wider, more complex and multi-zoned dike with a N20 [degrees] E strike, containing coarsely crystalline amazonite, topaz, smoky quartz, zinnwaldite and ferroan lepidolite [ILLUSTRATION FOR FIGURE 3 OMITTED].
And all Perthites shake their head about local real estate prices.