perthitic


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Related to perthitic: Poikilitic

perthitic

[pər′thid·ik]
(geology)
Of a texture produced by perthite, exhibiting sodium feldspar as small strings, blebs, films, or irregular veinlets in a host of potassium feldspar.
References in periodicals archive ?
The sample is a granular, medium-grained, pink granite composed mainly of quartz grains; perthitic potassium feldspar grains up to 0.
The patch- and vein-type perthitic inclusions in microclinic feldspar have the same composition.
The mineral composition of granites is evidently peralkaline from mineralogical point of view, manifested not only by the alkaline composition of their amphiboles and the perthitic one-feldspar character, but by the occurrence of symptomatic alkali granite rare accessory minerals as astrophyllite and plumbomicrolite and by special zircone habit with very short prismatic form as well.
Also among the basement rocks is the Devonian Petit-de-Grat Granite containing a distinctive perthitic texture (White et al.
The granite is generally grey to grayish white, essentially composed of perthitic feldspar, quartz and small amount of plagioclase and sodic minerals such as riebeckite and aegirine.
Although some dealers have said that the crystals occur in pockets in alkaline pegmatites, the pockets more nearly resemble alpine veins in a number of ways: alpine veins typically occur in gneissic rocks like the rocks at Zagi, but pocket pegmatites are more typical of coarse-grained, massive intrusive rocks; there is no development of pegmatitic textures such as graphic intergrowths or sudden coarsening of grains in the rock on the walls of the pockets; the common feldspar is translucent adularia, characteristic of alpine veins, rather than the more opaque perthitic microcline found in pegmatite pockets; and finally, the rare minerals are more typical of alpine veins than of pegmatites.
Primary phases in the leucogranite are dominantly perthitic K-feldspar, quartz, and plagioclase, and in the syenogranite, K-feldspar, quartz, and plagioclase.
The Utla granites contain phenocrysts of zoned and saussuritized plagioclase, perthitic alkali feldspar, including both the orthoclase and microcline varieties, and quartz.
In June 2003 this place produced fair numbers of blocky microcline crystals to 12 cm with bases merging into a "graphic" perthitic granite.
They are composed of euhedral to subhedral, coarsely perthitic alkali feldspar and varying amounts of interstitial quartz (Fig.
The mine also occasionally produces specimens of both aquamarine and morganite beryl, spessartine, topaz, apatite, and large, well-formed crystals of perthitic microdine.
In thin section, large perthitic K-feldspar megacrysts are in a hypidiomorphic granular matrix of normal to oscillatory zoned oligoclase, perthitic orthoclase-microcline, quartz, dark brown to orange-brown biotite, pinitized cordierite, and minor muscovite.