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[pley-jee-uh-kleys] /ˈpleɪ dʒi əˌkleɪs/
any of the feldspar minerals varying in composition from acidic albite, NaAlSi 3 O 8 , to basic anorthite, CaAl 2 Si 2 O 8 , found in most igneous rocks: shows twinning striations on good cleavage surfaces.
Also called soda-lime feldspar.
Origin of plagioclase
First recorded in 1865-70; plagio- + -clase
Related forms
[pley-jee-uh-klas-tik] /ˌpleɪ dʒi əˈklæs tɪk/ (Show IPA),
adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for plagioclase


a series of feldspar minerals consisting of a mixture of sodium and calcium aluminium silicates in triclinic crystalline form: includes albite, oligoclase, and labradorite
Derived Forms
plagioclastic (ˌpleɪdʒɪəʊˈklæstɪk) adjective
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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Word Origin and History for plagioclase

"triclinic feldspar," 1868, from German, coined 1847 by German mineralogist Johann Friedrich August Breithaupt (1791-1873) from plagio- + Greek klasis "fracture," from stem of klan "to break" (see clastic). Related: Plagioclastic.

Online Etymology Dictionary, © 2010 Douglas Harper
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plagioclase in Science
Any of a series of common feldspar minerals, consisting of differing mixtures of sodium and calcium aluminum silicates. Plagioclase is typically white, yellow, or reddish-gray, but it can also be blue to black. It occurs in igneous rocks. The minerals albite, oligoclase, andesine, labradorite, bytownite, and anorthite are all plagioclases. Chemical formula: (Na,Ca)Al(Si,Al)Si2O8.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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