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 (ŏl′ĭ-gō-klās′, -klāz′, ō′lĭ-)
A white, gray, green or red variety of plagioclase feldspar that contains a higher proportion of sodium than calcium and is common in silica-rich igneous rocks.

[oligo- + Greek klasis, cleavage (from klān, to break; see plagioclase feldspar).]


(Minerals) a white, bluish, or reddish-yellow feldspar mineral of the plagioclase series, consisting of aluminium silicates of sodium and calcium. Formula: NaAlSi3O8.CaAl2Si2O8
[C19: from oligo- + -clase]


(ˈɒl ɪ goʊˌkleɪs)

a plagioclase feldspar occurring in white, gray, greenish, or reddish crystals.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.oligoclase - any of a series of triclinic feldspars that form rocks
dacite - a grey volcanic rock containing plagioclase and quartz and other crystalline minerals
basalt - the commonest type of solidified lava; a dense dark grey fine-grained igneous rock that is composed chiefly of plagioclase feldspar and pyroxene
feldspar, felspar - any of a group of hard crystalline minerals that consist of aluminum silicates of potassium or sodium or calcium or barium
albite, white feldspar - a widely distributed feldspar that forms rocks
anorthite - rare plagioclastic feldspar occurring in many igneous rocks
References in periodicals archive ?
Euhedral to subhedral zoned oligoclase to andesine plagioclase (30% to 40%) and anhedral quartz (20% to 30%), in small pods, are the primary constituents of the rock.
Day and his colleagues immediately recognized that these meteorites were unusual because of elevated contents of a light-colored feldspar mineral called oligoclase.
Plagioclase is often replaced by alkali feldspar and varies in composition from andesine to oligoclase.
The core composition for all three types of crystals, as determined mainly by extinction angle methods, is bytownite for units A, C, E and G; labradorite for unit B and oligoclase for unit D.