• synonyms


[awr-thuh-kleys, -kleyz]
  1. a common white or pink mineral of the feldspar group, KAlSi3O8, having two good cleavages at right angles, and found in silica-rich igneous rocks: used in the manufacture of porcelain.
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Origin of orthoclase

1840–50; ortho- + -clase < Greek klásis cleavage, breaking
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for orthoclase

Historical Examples of orthoclase

  • In syenite and greenstone it occurs more commonly than orthoclase.


    James Geikie

  • This curve would represent the conditions under which orthoclase is in equilibrium with the molten magma.

  • If the initial composition of the magma is represented by a point between the two eutectic points, orthoclase will separate first.

  • The china-clay rocks of Cornwall and Devon are granites in which the orthoclase has become kaolinized.

  • The turbidity of orthoclase is usually due to partial kaolinization.

British Dictionary definitions for orthoclase


  1. 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: KAlSi 3 O 8 . Crystal structure: monoclinic
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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

orthoclase in Science


  1. A white to yellowish red monoclinic mineral of the potassium feldspar group that forms from medium- to low-temperature magmas. Chemical formula: KAlSi3O8.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.