groundmass

American  

[ground-mas] / ˈgraʊndˌmæs /

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.

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groundmass British  

/ ˈɡraʊndˌmæs /

noun

1. the matrix of igneous rocks, such as porphyry, in which larger crystals (phenocrysts) are embedded

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Etymology

Origin of groundmass

First recorded in 1875–80; ground ¹ + mass

Example Sentences

See Examples For:

groundmass

The large crystals are called phenocrysts and the fine-grained matrix is called the groundmass or matrix.

From Textbooks ● Jan. 1, 2017

Typically, smaller sediment grains, collectively called groundmass or matrix, fill in much of the volume between the larger clasts, and hold the clasts together.

From Textbooks ● Jan. 1, 2017

This sample is mostly fine groundmass with a few small green phenocrysts that are the mineral olivine.

From Textbooks ● Jan. 1, 2017

Olivine rarely occurs as an ingredient of the groundmass.

From Encyclopaedia Britannica, 11th Edition, Volume 3, Part 1, Slice 3 "Banks" to "Bassoon" by Various

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

From The Long Labrador Trail by Dillon Wallace