phenocryst

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phenocryst

[′fēn·ə‚krist]
(petrology)
A large, conspicuous crystal in a porphyritic rock. Also known as phanerocryst.
References in periodicals archive ?
The bombs have a hypocrystalline, porphyritic, highly vesicular (50%) texture with plagioclase, clinopyroxene, orthopyroxene, and olivine phenocrysts in an intersertal matrix (Figs.
Its age and the presence of potassium-feldspar phenocrysts (1 to 2 cm in length) suggest that the granitic dyke is an offshoot of the nearby Magaguadavic pluton.
Some of the latter contain plagioclase phenocrysts nearly totallysaussuritized (epidote + white mica), with or without altered mafic minerals including biotite, in an altered groundmass of cloudy/saussuritized plagioclase, amphibole, chlorite, biotite, ilmenite, +/- titanite/leucoxene, calcite (abundant in a few), quartz, and rare serpentine, chalcedony(?
4575 was porphyritic medium-grained biotite-amphibole granodiorite with the occurrence of feldspar phenocrysts up to 1.
7A); and b) banded vesicular lavas having a fluidal laminated texture and different vesicular density, with forsterite phenocrysts (Figs.
The texture of andesite is generally porphyritic, with phenocrysts of feldspar and ferromagnesian minerals.
Alteration of both phenocrysts and groundmass is also evident in most sections, with olivine partly or totally altered to iddingsite, and plagioclase weathering to clay minerals.
Mafic volcanic rocks are dominantly basaltic and typically contain augite and plagioclase phenocrysts.
Porphyrite" is a term "originally used to distinguish porphyries that contain plagioclase phenocrysts from those that contain alkali feldspar phenocrysts" (Jackson, 1997).
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.