What is the difference between granite and porphyry?

Category: Question and Answer Updated: 2023/11/8

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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.

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