groundmass

American

[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.

groundmass British

/ 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

Etymology

Origin of groundmass

First recorded in 1875–80; ground ¹ + mass

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

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

From Scientific American

Olivine rarely occurs as an ingredient of the groundmass.

From Project Gutenberg

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

From Project Gutenberg

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023