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.

Nearby words

  1. plagiarist,
  2. plagiarize,
  3. plagiary,
  4. plagio-,
  5. plagiocephaly,
  6. plagioclimax,
  7. plagiohedral,
  8. plagiotropic,
  9. plagiotropism,
  10. plague

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



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

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

Science definitions for plagioclase



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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.