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Related to groundmass: mafic, Phaneritic, vesicular


The fine-grained crystalline base of porphyritic rock in which larger crystals are embedded.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(Geological Science) the matrix of igneous rocks, such as porphyry, in which larger crystals (phenocrysts) are embedded
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014



the crystalline, granular, or glassy base or matrix of a porphyritic or other igneous rock, in which the more prominent crystals are embedded.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
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
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References in periodicals archive ?
The Phenocrysts in the granite is feldspar and quartz however, the groundmass consists of Perthtized alkali feldspar, quartz, muscovite and biotite.
The fragments are commonly covered by thin coatings of clayey material, with a different composition than the groundmass, and some fragments show truncation of internal planar features.
Its reason of anomaly is possibly from change of the plumb line due to the motion of the groundmass before earthquake (Zhang, 1981).
A detailed microanalytical geochemical and in situ Sr-isotope study performed on glassy groundmass of single ash clast showed unusually high [sup.87]Sr/[sup.86]Sr values (up to 0.70668) for Icelandic volcanism (0.7026-0.7037 [94]) (Figure 8(c)); these high isotopic values were also associated to atypical elemental compositions compared to most of the juvenile ash fragments of the eruption.
The groundmass contains microlites of plagioclase, amphibole, abundant magnetite crystals, and felsic glass.
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.
In order to better position the isolated occurrence of the Baltic dolerite sills in the geological evolution of the region, we used the obtained new [sup.40]Ar/[sup.39]Ar dating results of a whole-rock and a groundmass plagioclase sample in combination with whole-rock major and trace element data.
Boulis and Attia found that the anatase presents as very fine Ti-bearing grains disseminated throughout the kaolinite groundmass. (19) Calcination of KF pigment up to 900[degrees]C reduced LOI from 13.92 to 0.78 due to dehydration and dehydroxylation of kaolinite to produce metakaolinite, which is the most active form of kaolinite (Table 2.) The bleaching of metakaolinite (Cal K/d) reduced the iron oxide content from 0.24 to 0.12 (wt%).
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. Phlogopite and diopside are mainly present in holocrystalline rocks as subhedral and euhedral crystals (Fig.