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 ?
The finest (< 5 [micro]m) groundmass serves as a matrix for scattered grains > 5 [micro]m in size.
Many of the river cobbles collected often had very irregular surfaces, where the phenocrysts jut out from the eroded groundmass.
In addition, powder x-ray diffraction analysis of a coprolite sample indicates that the groundmass consists of calcium phosphate.
This breccia consists of a groundmass of chrysotile [+ o -] antigorite [+ o -] chlorite within which irregular millimetric--to decametric-sized bodies of serpentinized harzburgite appear here and there.
It is characterized by a wide range of very low-grade, low-grade, and rare medium-grade metamorphic rock fragments, set in a groundmass rich in mica laths and quartz grains.
Despite the inclusion of statements such as 'all contain sanidine in the groundmass as well as significant amounts of plagioclase .
Anil points out that "Webster's 2nd defines pilandite as 'a leucocratic porphyry with phenocrysts, a groundmass of anorthoclase, and a little amphibole" and adds "Well at least I know what 'a', 'with', 'of', 'and', and 'little' mean.
They have a speckled, densely granular appearance due to a combination of colorless lipid droplets, <6 [micro]m diameter, set in a magenta-stained yolk groundmass.
The groundmass often contains plagioclase phenocrysts, several millimetres, sometimes up to 1 cm in size.
The most common groundmass texture is intergranular, with seriate, very fine- to coarse-grained, finely albite twinned and tapered labradorite laths, stubby augite prisms, subequant olivine grains and platy to equant opaque grains.