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groundmass

groundmass The finer-grained material of igneous rocks in which larger crystals (phenocrysts) and xenoliths are enclosed. The groundmass of an igneous rock commonly represents that part of the magma system which has cooled rapidly. Rapid cooling initiates numerous crystal nucleation sites which limit the size to which crystals can grow. In lavas, the fine ground-mass is formed when the magma is erupted on to the Earth's surface and is cooled rapidly by air convection over the flow. Compare MATRIX.

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"groundmass." A Dictionary of Earth Sciences. . Encyclopedia.com. 22 Aug. 2017 <http://www.encyclopedia.com>.

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"groundmass." A Dictionary of Earth Sciences. . Retrieved August 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/groundmass

groundmass

groundmass: see porphyry.

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"groundmass." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 22 Aug. 2017 <http://www.encyclopedia.com>.

"groundmass." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (August 22, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/groundmass

"groundmass." The Columbia Encyclopedia, 6th ed.. . Retrieved August 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/groundmass