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A plagioclase feldspar mineral with a composition ranging from Ab90 An10 to Ab70 An30, where Ab = NaAlSi3O8 and An = CaAl2O8.



a rock-forming mineral of the feldspar (plagio-clase) group; an isomorphous mixture of 10–30 percent anorth-ite, Ca[Al2Si2O8], and 70–90 percent albite, Na[AlSi3O8].

References in periodicals archive ?
The mineral assemblage is composed of ande-sine to oligoclase and Na-sanidine laths, small amount of ferromagnesian minerals (predominantly clinopy-roxene and kaersutite), and zeolite pseudomorphs after feldspathoid(s).
In thin section (Figure 16) some of these phenocrysts are pokilocrysts with an oligoclase nucleus (Figure 16 B).
Under different nucleation, diffusion and growing rates, augite-aegirine, sphene, zircon, oligoclase, anorthoclase and sanidine could crystallize in the intratelluric environment.
5 mm in size correspond to oligoclase or oligoclae-andesine respectively.
1 to 1 mm in size corresponds to oligoclase, potassium feldspar occurs sporadically.
Those in the southeast preserve common staurolite-garnet-biotite assemblages, whereas staurolite appears in association with oligoclase porphyroblasts in the northwest.
Normally zoned plagioclase phenocrysts are oligoclase on average ([An.
Commonly, nearly all the amphibole is blue green and the accompanying plagioclase compositions range from oligoclase to andesine.
1) Rutite [rightarrow] Zircon [rightarrow] Monazite [rightarrow] Ilmenite [rightarrow] Magnetite [rightarrow] Spessartine [rightarrow] Biotite [rightarrow] Muscovite [rightarrow] Oligoclase [rightarrow] Orthoclase [rightarrow] Quartz
The Sedgwick Granite is a grey, medium- to coarse-grained, equigranular, biotite granite that contains 35% microcline, 32% quartz, 28% oligoclase, 4% biotite, and trace amounts of zircon, apatite, and titanite.
Due to their being embedded in oligoclase near annite contacts, no important matrix specimens were recovered.