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)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The finest (< 5 [micro]m) groundmass serves as a matrix for scattered grains > 5 [micro]m in size.
The [sup.40]Ar/[sup.39]Ar analysis of groundmass plagioclase sample D1-1 was carried out at the Vrije Universiteit (VU) in Amsterdam using the VULKAAN [sup.40]Ar/[sup.39]Ar C[O.sub.2] laser probe and a MAP 215-50 double focusing noble gas mass spectrometer fitted with a Johnston MM1 secondary electron multiplier detector (Wijbrans et al.
The andesites of Noorabad ophiolite in hand specimen and thin section have phenocrysts of plagioclase in a groundmass of clinopyroxene and amphibole minerals.
The groundmass surrounding the glass clasts and crystal fragments seem to be flushed with organic matter with different sizes and structures showing different degrees of biodegradation and alteration to amorphous organic matter (AOM).
The hypocrystalline groundmass contains clinopyroxene (39-46 vol%, Mg# ~0.75), olivine (3-6vol%, [Fo.sub.74-76] mole%), titanomagnetite (4-7vol%, up to 43% ulv.
Many of the river cobbles collected often had very irregular surfaces, where the phenocrysts jut out from the eroded groundmass.
In addition to these visual observations, a powder x-ray diffraction analysis was run on one coprolite specimen to determine the major composition of its groundmass.
The respective values for the groundmass of the inside-crater crystalline-derived breccia matrix range from -27.30 [per thousand] to -28.35 [per thousand], and is -25.70 [per thousand] for the magnetic particles.
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 ...