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groundmass

[ ground-mas ]

noun

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


groundmass

/ ˈɡraʊndˌmæs /

noun

  1. 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


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Word History and Origins

Origin of groundmass1

First recorded in 1875–80; ground 1 + mass
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Example Sentences

The felted or hyalopilitic texture is the most common, and plagioclase is the principal groundmass constituent.

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

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

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

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ground loopground meristem