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[awr-thuh-kleys, -kleyz] /ˈɔr θəˌkleɪs, -ˌkleɪz/
a common white or pink mineral of the feldspar group, KAlSi 3 O 8 , having two good cleavages at right angles, and found in silica-rich igneous rocks: used in the manufacture of porcelain.
1840-50; ortho- + -clase < Greek klásis cleavage, breaking Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for orthoclase
  • These large crystals are minerals in the feldspar family, namely the alkali feldspars orthoclase and microcline.
  • The pink mineral is called orthoclase, a member of the mineral family feldspar.
  • There is also some variation in the amount of quartz present, and in the relative importance of the orthoclase and plagioclase.
  • Granite--Naturally igneous rock formed of crystallized quartz and orthoclase.
British Dictionary definitions for orthoclase


/ˈɔːθəʊˌkleɪs; -ˌkleɪz/
a white to pale yellow, red, or green mineral of the feldspar group, found in igneous, sedimentary, and metamorphic rocks. It is used in the manufacture of glass and ceramics. Composition: potassium aluminium silicate. Formula: KAlSi3O8. Crystal structure: monoclinic
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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orthoclase in Science
A white, pink, yellow, or brown type of potassium feldspar. It is dimorphous with microcline, being more stable at higher temperatures than it is. Also called: potash feldspar. Chemical formula: KAlSi3O8.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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