plagioclase definition | Dictionary.com

pla⋅gi⋅o⋅clase

[pley-jee-uh-kleys]

–noun

any of the feldspar minerals varying in composition from acidic albite, NaAlSi₃O₈, to basic anorthite, CaAl₂Si₂O₈, found in most igneous rocks: shows twinning striations on good cleavage surfaces.

Also called soda-lime feldspar.

Origin:
1865–70; plagio- + -clase

Related forms:

pla⋅gi⋅o⋅clas⋅tic [pley-jee-uh-klas-tik]

, adjective

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Based on the Random House Dictionary, © Random House, Inc. 2009.
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pla·gi·o·clase (plā'jē-ə-klās', -klāz', plāj'ē-)

n. Any of a common rock-forming series of triclinic feldspars, consisting of mixtures of sodium and calcium aluminum silicates. Also called oligoclase.

[Greek plagio-, plagio- + Greek klasis, breaking (from its oblique cleavage) (from klān, to break).]

The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2009 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Plagioclase

Pla"gi*o*clase\, n. [Gr. ? oblique + ? to break.] (Min.) A general term used of any triclinic feldspar. See the Note under Feldspar.

plagioclase (plā'jē-ə-klās') Pronunciation Key
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.

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