Porphyry (geology)

A porphyry is an igneous rock with large, prominent crystals embedded in a much finer-grained groundmass.

The larger crystals are called phenocrysts.

Porphyry is a rock structure; it's chief characteristic is a large difference between the size of the groundmass crystals and other much larger crystals.

Porphyries may be aphanites or phanerites, that is, the groundmass may have invisibly small crystals, like basalt, or the individual crystals of the groundmass may be easily distinguished with the eye, as in granite.

Many types of igneous rocks may display porphyry.

Example Porphyries

• Diorite porphyry
• Granite porphyry
• Ryolite porphyry