PORPHYRITIC GRANITE
Porphyritic granite has the same chemistry & mineralogy as ordinary
granite, but differs in the size range of its crystals. Granites are
coarsely crystalline igneous rocks, having a phaneritic texture.
Porphyritic granites have a mix of large & small crystals, but all crystals
are still fairly decent-sized.
Large crystals in a porphyritic rock are called phenocrysts.
The smaller crystals make up the groundmass. Porphyritic granites
typically have K-feldspar phenocrysts (pinkish). The groundmass is
typically quartz (grayish), sodic plagioclase feldspar (whitish-gray), amphibole
(black), plus sometimes biotite mica and/or muscovite mica.
Porphyritic granite