Also found in: Thesaurus, Encyclopedia, Wikipedia.
Related to groundmass: mafic, Phaneritic, vesicular


The fine-grained crystalline base of porphyritic rock in which larger crystals are embedded.


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



the crystalline, granular, or glassy base or matrix of a porphyritic or other igneous rock, in which the more prominent crystals are embedded.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.groundmass - (geology) the matrix of fine-grained crystalline material in which larger crystals are embedded
geology - a science that deals with the history of the earth as recorded in rocks
igneous rock - rock formed by the solidification of molten magma
porphyritic rock, porphyry - any igneous rock with crystals embedded in a finer groundmass of minerals
References in periodicals archive ?
The dominating biogenic compounds are: (i) calcite as < 5 m[micro] micrite forming the groundmass mudstone, and both micrite of the matrix and > 5 m[micro] to 1 mm grains--skeletal particles (shells and their broken fragments) in wackestone, (ii) silica as < 5 m[micro] particles belonging to the groundmass of mudstone and wackestone matrix, (iii) organic matter (kerogen) in the mudstone and matrix of wackestone, (iv) phosphate skeletal fragments in certain interbeds of wackestone and very fine apatite in groundmass.
Some of the latter contain plagioclase phenocrysts nearly totallysaussuritized (epidote + white mica), with or without altered mafic minerals including biotite, in an altered groundmass of cloudy/saussuritized plagioclase, amphibole, chlorite, biotite, ilmenite, +/- titanite/leucoxene, calcite (abundant in a few), quartz, and rare serpentine, chalcedony(?
Boulis and Attia found that the anatase presents as very fine Ti-bearing grains disseminated throughout the kaolinite groundmass.
Olivine almost disappears in the holocrystalline inner parts of the lamproitic main body, but is locally common in the glassy lavas where there is a porphyric texture with glassy to microcrystalline groundmass.
The pillow lavas have microvesicles that are filled with chlorite; carbonate and opaque minerals that located in a groundmass of plagioclase and clinopyroxene microlites.
The first exhibit balls (tephra balls) composed of a mixture of glassy porphyritic basalt fragments, crystal fragments of olivine, pyroxenes and zeolitized plagioclase admixed with organic matter, set in a groundmass of finer calcareous muddy material with crystal fragments, clays, analcime, calcite and organic matter.
Hydraulic conductivity of saprolite as determined by channels and porous groundmass.
Phenocryst-free groundmass from the Media Luna sample was incrementally heated in a double-vacuum resistance furnace attached to a 300 cm3 gas clean-up line following the procedures of Jicha (2009).
Absyctos has a black groundmass cut by red veins while nasamonites has a red groundmass cut by black veins.