from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The fine-grained crystalline base of porphyritic rock in which larger crystals are embedded.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The matrix of fine-grained crystalline material in which larger crystals are embedded.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. (geology) the matrix of fine-grained crystalline material in which larger crystals are embedded
The rock here is a porphyritic granite (porhyritic meaning that the stone has large-grained crystals, such as feldspar or quartz, dispersed in a fine-grained feldspathic matrix or groundmass).
[Small, separated mineral crystals in a glassy groundmass]
Immersed in this groundmass are a wide variety of rock shapes, sizes, textures—round and angular—many with varying consistencies.
The groundmass throughout the area is a very fine sand to a silt.
Liquid (l) is seen at the bottom right, the rest being vapor (v). (g) Primary vapor-rich inclusion at the tip of a quartz stringer (outlined for clarity) in the granophyric groundmass.
Radiating fringe of feldspar in groundmass is in optical continuity with phenocryst, from which it nucleated. (e) Quartz phenocryst is surrounded by feldspar groundmass.
Quartz in groundmass does not appear to have nucleated directly on phenocryst, but is in optical continuity with it. (f) Primary vapor-rich fluid inclusion in phenocrystic quartz.
Figure parts a-e with crossed nichols. (a) Micrographic groundmass surrounds feldspar phenocryst fragment. (b) Micrographic groundmass around clinopyroxene phenocryst.
K/Na of the groundmass feldspar equals K/Na in pumiceous glass of the host pumice, hinting that the granophyric minerals grew by closed-system crystallization of the rhyolitic melt.
Granophyric intergrowths of quartz and feldspar in the groundmass contain abundant, primary, vapor-rich fluid inclusions, 1 to 10 µm in diameter.
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