aphanitic


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aphanitic

[‚af·ə′nid·ik]
(petrology)
Referring to the texture of an igneous rock in which the crystalline components are not distinguishable by the unaided eye.
References in periodicals archive ?
Ls = sedimentary aphanitic lithic grains + extrabasinal carbonate
L = Lvm + Lsm###where###Lvm = volcanic, hypabasal and metavolcanic aphanitic lithic grains
4h) is medium grey, and has hornblende phenocrysts ranging from 3 to 5 mm in size in an aphanitic groundmass.
The aphanitic variety displays a typical trachytic texture with flow-aligned feldspars (0.
The matrix is composed of an aphanitic quartz-feldspar mosaic.
However, contacts between coarse and fine-grained to aphanitic felsic rocks are always sharp where exposed, and where intrusive relations can be determined, the coarse-grained phase invariably cuts the fine-grained one.
It is reasonable to conclude that in the case of the San Martino porphyry with its aphanitic matrix, the coarser grain size of the more mafic enclaves suggests that they arrived as solids or near-solids (crystal mushes) rather than crystallizing after emplacement even at the level of the deepest feeder dykes.
They are commonly intruded by aphanitic diabase with plagioclase porphyritic interiors.
5-foot thick aphanitic layer of calcarenitic limestone, commonly marly and fossi-liferous; (2) a 233-foot thick aphanitic limestone; and (3) a 110.
The subvolcanic rhyolite porphyry has a red, aphanitic matrix and typically contains small rounded quartz phenocrysts and feldspar laths.
Venugopal (1979) reported that the rhyolite contains plagioclase, alkali feldspar, and embayed quartz phenocrysts set in a partially sericitized, aphanitic groundmass; a late phase of devitrification is indicated by oval patches of radiating plagioclase scattered throughout the finer groundmass.