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

Word History and Origins

Origin of groundmass¹

First recorded in 1875–80; ground ¹ + mass

Example Sentences

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

Read more on Scientific American

Olivine rarely occurs as an ingredient of the groundmass.

Read more on Project Gutenberg

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

Read more on Project Gutenberg