Porphyritic Rock
"Just like pegmatite, porphyritic
rock is a term that describes a rock's texture rather than
composition."
But unlike pegmatite, porphyry does not only mean that the rock has large crystals, it means it has large crystals in a fine-grained matrix - that's both large and very small crystals in the same rock.
Those large crystals are called phenocrysts, and they have formed before the matrix that surrounds them.
Many rocks can be porphyritic, such as andesite porphyry, rhyolite porphyry, basalt porphyry and many, many ohters.
Granite porphyry. By Fool-On-The-Hill
Back to Types of Igneous Rocks
