[ pley-jee-uh-kleys ]
/ ˈpleɪ dʒi əˌkleɪs /


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.

Origin of plagioclase

First recorded in 1865–70; plagio- + -clase
Also called soda-lime feldspar.
Related formspla·gi·o·clas·tic [pley-jee-uh-klas-tik] /ˌpleɪ dʒi əˈklæs tɪk/, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for plagioclase

British Dictionary definitions for plagioclase


/ (ˈpleɪdʒɪəʊˌkleɪz) /


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 Formsplagioclastic (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

Science definitions for plagioclase


[ plājē-ə-klās′ ]

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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