Cao et al., "Selective dissolution of
alkali feldspars and its effect on Lower Triassic sandy conglomerate reservoirs in the Junggar Basin, northwestern China," Geological Journal, vol.
###11La(W)###Coarse###Angular-###Moderately###Grain###Ferruginous###Plagioclase,
alkali Feldspar,
Quartz is low to moderate in abundance and feldspar is in significant proportion with plagioclase:
alkali feldspar ratio high.
Alkali feldspars are represented by orthoclase and microcline.
They contain clinopyroxene ([Wo.sub.43-50][Fs.sub.6-14]), olivine ([Fo.sub.43-82]), Ti-biotite, Ti-magnetite [+ or -] ilmenite, plagioclase ([An.sub.31-78]),
alkali feldspar ([Or.sub.60-84]), interstitial nepheline-analcime ([Ne.sub.37-82][Ks.sub.15-23]), and
alkali feldspar ([Or.sub.80-97]).
The
alkali feldspar, including microcline, is mostly perthitic and occurs as megacrysts that occasionally display simple twinning (Figures 3(a) and 3(b)).
In these zones, few of the primary igneous features are preserved, but the rocks appear to have been coarse grained, with abundant quartz and
alkali feldspar (Fig.
The degree of porosity depends on the composition of the parent feldspar grain, with plagioclase producing a dense clay matrix and
alkali feldspar a highly porous clay matrix.
It has a typical rapakivi texture with
alkali feldspar megacrysts (ovoids) mantled by plagioclase.
Acid igneous rock fragments: composed of quartz,
alkali feldspar, plagioclase feldspar, and occasional muscovite/and or biotite mica, amphibole, and microcline.
Different aliquots were dated, and for the control quartz was used parallel to
alkali feldspars. 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.
and Stewart, D.B., 1968, X-ray and optical study of
alkali feldspar: I.
