groundmass

[ ground-mas ]
/ ˈgraʊndˌmæs /
|

noun

the crystalline, granular, or glassy base or matrix of a porphyritic or other igneous rock, in which the more prominent crystals are embedded.

Nearby words

  1. grounding,
  2. groundkeeper,
  3. groundless,
  4. groundlessly,
  5. groundling,
  6. groundnut,
  7. groundnut oil,
  8. groundout,
  9. groundplot,
  10. grounds

Origin of groundmass

First recorded in 1875–80; ground1 + mass

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for groundmass

  • Pyroxene, quartz and augite form the groundmass, as seen in section.

  • These lavas have groundmass textures that vary from almost holo-crystalline to glassy.

  • In a basal flow in Moraine Park, the slaggy and compact phases show differences in phenocrysts as well as in groundmass.



British Dictionary definitions for groundmass

groundmass

/ (ˈɡraʊndˌmæs) /

noun

the matrix of igneous rocks, such as porphyry, in which larger crystals (phenocrysts) are embedded
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