alkali feldspar


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Related to alkali feldspar: Plagioclase feldspar, quartz, hornblende, K feldspar

alkali feldspar

n.
Any of a series of feldspars, consisting primarily of a mixture of sodium aluminum silicate, NaAlSi3O8, and potassium aluminum silicate, KAlSi3O8.
References in periodicals archive ?
They are composed of euhedral to subhedral, coarsely perthitic alkali feldspar and varying amounts of interstitial quartz (Fig.
The separated but matching adjacent grain boundaries in fractured quartz and residual alkali feldspar grains in saprolite are indicative of minor pedoplasmation.
As a rule, the alkali feldspar measurements give somewhat higher ages than OSL from quartz, which can be explained by slower bleaching of the feldspar in the sunlight exposure.
39]Ar age determinations on single crystals of alkali feldspar extracted from pumices found at the top of the blue tuff show that it was deposited 1,468,000[+ or -]16,000 years ago (Stern et al.
The dyke a]so contains abundant phenocrysts and cognate xenocrysts of kaersutite, biotite, and magnetite, and xenocrysts of a]bite and alkali feldspar.
Below the cover of glacial till, a series of interbedded sands and shales contain abundant igneous minerals: fresh angular grains of plagioclase, alkali feldspar, quartz, hornblende, pyroxene, garnet, sphene, magnetite and other opaque minerals and wte, highly kaolinized shale beds contained biotite flakes.
Alkali feldspar occurs as interstitial grains or antiperthitic inclusions in plagioclase.
This difference is most readily explained by the crystallization of Ca-bearing plagioclase and clinopyroxene in the trachyte magma, and alkali feldspar crystallization in the rhyolite magma.
Digital images of rock slabs were analyzed to determine proportions of matrix and quartz and alkali feldspar phenocrysts.
This episode started with emplacement of the Capo Bianco porphyritic aplite, with alkali feldspar granite composition, followed by the Nasuto micro-syenogranite.
One of the most complex pegmatites in the region was selected for study in order to investigate the genetic relationship of the dyke to the nearby alkali feldspar granite, to determine the internal evolution of the pegmatite, and to estimate the physical and chemical properties of the pegmatite-forming fluid.