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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 groundmass they're in speaks of fairly rapid cooling and low pressure conditions.

Olivine rarely occurs as an ingredient of the groundmass.

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

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ground loopground meristem