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

From Project Gutenberg

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

From Project Gutenberg

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

From Project Gutenberg

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

From Project Gutenberg