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A conspicuous, usually large, crystal embedded in porphyritic igneous rock.

phe′no·crys′tic adj.


(ˈfiːnəˌkrɪst; ˈfɛn-)
(Geological Science) any of several large crystals that are embedded in a mass of smaller crystals in igneous rocks such as porphyry
[C19: from pheno- (shining) + crystal]


(ˈfi nə krɪst, ˈfɛn ə-)

any of the conspicuous crystals in a porphyritic rock.
[1890–95; pheno- + cryst (al)]
References in periodicals archive ?
7) indicate fractional crystallization of mafic minerals and early fractionation of plagioclase, the latter being in agreement with the presence of plagioclase phenocrysts.
The andesites of Noorabad ophiolite in hand specimen and thin section have phenocrysts of plagioclase in a groundmass of clinopyroxene and amphibole minerals.
The dyke rock has a distinctive cross-columnar field appearance, and a subophitic to micro-porphyritic texture with abundant Ti-bearing augite, calcic plagioclase, scattered euhedral orthopyroxene phenocrysts, and coarse-grained glomerophyric clumps of augite with plagioclase.
Contained within the bentonites are remnant diagnostic mineral phenocrysts that are unique to the composition of each volcanic ash deposit.
The texture of andesite is generally porphyritic, with phenocrysts of feldspar and ferromagnesian minerals.
5% sulphides mainly chalcopyrite with molybdenum both as fine grained clusters in chlorite-biotite aggregates and as fine-medium grained clusters within 10% quartz-biotite-sulphide stockwork stringers surrounded by halos of clay-altered phenocrysts in the intrusive.
Andesite-dacite dikes have a porphyritic microstructure and contains phenocrysts of zoned plagioclase, quartz, zoned hornblende and biotite.
Mafic volcanic rocks are dominantly basaltic and typically contain augite and plagioclase phenocrysts.
The mineralogy of the flows includes both phenocrysts of feldspar and quartz and extensive vapor phase minerals.
the presence of olvine and the lack of phenocrysts of sanidine rules out the Sabatini system' (a conclusion of the rubble study), the book aims to serve both a specialist and a general reader, and is generally successful in this.
Anil points out that "Webster's 2nd defines pilandite as 'a leucocratic porphyry with phenocrysts, a groundmass of anorthoclase, and a little amphibole" and adds "Well at least I know what 'a', 'with', 'of', 'and', and 'little' mean.
Francois Mountain rocks have several highly distinctive characteristics: high olivine content, characteristic plagioclase phenocrysts, and angular iron stained surfaces of columnar blocks extracted from intrusive dikes (Amos & Densborough 1970:16).