3.4.3 Igneous Textures: Porphyritic Rocks have Phenocrysts embedded in a Groundmass matrix
Channel: Snow Mountain
Date: 20/09/2020

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3.4.3 Igneous Textures: Porphyritic Rocks have Phenocrysts embedded in a Groundmass matrix

What is Porphyritic texture?  A large mass of magma located at depth may require tens to hundreds of thousands of years to solidify. Because different minerals crystallize at different temperatures, as well as different rates, it is possible for some crystals to become quite large before others even begin to form. If magma containing some large crystals should change environments, for example by erupting at the surface, the remaining liquid portion of the lava would cool relatively quickly. 

The resulting rock, which has large crystals embedded in a matrix of smaller crystals, is said to have a porphyritic texture. The large crystals in such a rock are referred to as phenocrysts, whereas the matrix of smaller crystals is called a groundmass. A rock with such a texture is termed a porphyry.

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