n. (pl. -ies)
1. a hard rock quarried in ancient Egypt, composed of crystals of white or red feldspar in a red matrix.
2 Geol. an igneous rock with large crystals scattered in a matrix of much smaller crystals.
Derivatives:
porphyritic adj.
Etymology: ME ult. f. med.L porphyreum f. Gk porphurites f. porphura purple