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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 ?
Overall, the blocks show a hypocrystalline, porphyritic texture with plagioclase, clinopyroxene, orthopyroxene, and olivine phenocrysts in an intersertal matrix (Figs.
Plagioclase (54%) forms heteroblastic and xenoblastic individuals, which constitute former phenocrysts or matrix of the protolith.
2008); the presence of large potassium feldspar phenocrysts indicates that the magma may have been sequestered in the deep crust for some time before rising and solidifying nearer to the surface (McLeod 1990).
One of these, a medium-grained gabbroid, contains up to 3 cm long phenocrysts of plagioclase.
The samples were porphyric coarse-grained biotite granite with the occurrence of feldspar phenocrysts up to 3 cm in size and directionless structure.
7) indicate fractional crystallization of mafic minerals and early fractionation of plagioclase, the latter being in agreement with the presence of plagioclase phenocrysts.
5) are usually angular and show different textures, from fluidal with phenocrysts of forsteritic olivine, to highly vesicular scoriaceous.
The hyalite-bearing layer is composed of 3-50 mm rhyolite rock fragments mixed with 1-4 mm dipyramidal fe-quartz and limpid sanidine phenocrysts in a weakly welded, porous, siliceous, tuffaceous matrix.
The andesites of Noorabad ophiolite in hand specimen and thin section have phenocrysts of plagioclase in a groundmass of clinopyroxene and amphibole minerals.
Contained within the bentonites are remnant diagnostic mineral phenocrysts that are unique to the composition of each volcanic ash deposit.