groundmass


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Related to groundmass: mafic, Phaneritic, vesicular

groundmass:

see porphyryporphyry
, igneous rock composed of large, conspicuous crystals (phenocrysts) and a groundmass in which the phenocrysts are embedded. Some authorities consider the expression "porphyritic rock" better usage than porphyry, since the term refers only to the texture of the
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groundmass

[′grau̇nd‚mas]
(analytical chemistry)
References in periodicals archive ?
3, bottom), the groundmass was relatively dense, with sub-horizontal and sub-vertical thin planes, and some irregular to rounded small voids.
Redeposited material is distinguished by the lack of parallel orientation and lamination of deposits, with the inclusions being embedded in a mixed ash and organic rich groundmass (Matthews 2005).
Microprobe analysis of the yellow organic groundmass indicates a higher clay content than in the black organic materials.
1 millimetre and less), light greyish yellow or bluish grey groundmass.
The groundmass is granophyric, partly spherulitic, and contains miarolitic cavities.
Hornblende occurs in some of the dikes as small needles in the groundmass or as large ragged grains.
Disseminated arsenopyrite and pyrite occurs in the groundmass of the porphyry and is related to the fracturing and subsequent alteration.
Plagioclase-rich groundmass is commonly overprinted by secondary phases and in a few localities, all primary features have been obscured.
At these three sites, the upper part of the lower unit represents a buried surface horizon, containing euhedral sparitic calcite crystals in the groundmass and in pores (Mees and Van Ranst 2011).
The primary mineralogy of komatiites is simple: phenocrysts of olivine and spinel/chromite (+/pyroxene) are enclosed in a groundmass composed of glass, calcic clinopyroxene and minor orthopyroxene.