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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 ?
Their highly reflective surfaces produce optical effects such as aventurescence in oligoclase, often called sunstone (Gubelin and Koivula, 1986, pp.
15 and that the granodiorite contains oligoclase (An = 23-28) and andesine (An = 30-36) plagioclase (Fig.
Plagioclase is cloudy to saussuritized in some rocks especially in the more calcic cores but where fresh it is of intermediate anorthite content (calcic oligoclase to andesine).
This is also supported by the presence of albite and oligoclase, oligoclase also indicating an intermediate volcanic source.
It is composed of feldspar, usually potash feldspar and oligoclase and quartz, with a small amount of mica and minor accessory minerals, such as zircon, apatite, magnetite, ilmenite and sphene.
The melanophyres of the Ilfeld Basin, which come from the earlier or earliest of the eruptive episodes, are brown to black, with a fine-grained groundmass composed of oligoclase, augite, biotite, apatite and magnetite, with phenocrysts, most of which are tabular crystals of augite (Luedecke, 1896).
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.
Product Overview II-3 Feldspar: A Common Silicate II-3 General Chemical Formula II-3 Na-Feldspars are Widely Used II-3 Physical Properties II-4 Grades II-4 Glass Grade II-4 Ceramic Body Grade II-4 Glaze Grade II-4 Types II-5 Potassium Feldspar Group II-5 Plagioclase Feldspar Group II-5 Other Feldspars II-5 Rare Feldspars II-5 Characteristics of Major Feldspar Minerals II-6 Albite (moonstone) II-6 Oligoclase Feldspar II-6 Anorthite II-7 Microcline II-7 Orthoclase II-8 History II-8 Feldspars as Gemstones II-8 Principal Stones in Feldspar Group II-9 Labradorite II-9 Moonstone II-9 Sunstone II-9 Amazonite II-9 Orthoclase II-10 Occurrence II-10 Ores and Production Process II-10 Places of Origin II-10 Production II-11