Also found in: Thesaurus, Encyclopedia, Wikipedia.


 (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).]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(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]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(ˈɒl ɪ goʊˌkleɪs)

a plagioclase feldspar occurring in white, gray, greenish, or reddish crystals.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
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
Based on WordNet 3.0, Farlex clipart collection. © 2003-2012 Princeton University, Farlex Inc.
References in periodicals archive ?
A total of 7 primary minerals, that is, quartz, kaolinite, illite, K-feldspar, arsenopyrite, calcite, and magnesite, were chosen, and another 5 secondary minerals (chlorite, dolomite, goethite, oligoclase, and smectite-Ca) were expected to be precipitated (Table 2).
The element analysis of the marked crystals resembled erionite and oligoclase. From microstructural observations, it could be said that the selected matrices are not homogeneous (Figures 4(b)-4(c)).
Their highly reflective surfaces produce optical effects such as aventurescence in oligoclase, often called sunstone (Gubelin and Koivula, 1986, pp.
These data indicate that the plagioclase has An values of 23.02-36.15 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).
In addition, the mineralogical composition of the feldspar was determined from X-ray diffractogram (Figure 2(a)), and the following mineral phases were identified: oligoclase, quartz, illite, and calcite.
This is also supported by the presence of albite and oligoclase, oligoclase also indicating an intermediate volcanic source.
Subhedral grains of plagioclase (oligoclase) often show zoning caused by slight chemical variations.
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.