Porphyry \Por"phy*ry\, n.; pl. Porphyries. [F. porphyre, L. porphyrites, fr. Gr. ? like purple, fr. ? purple. See Purple.]

(Geol.) A term used somewhat loosely to designate a rock consisting of a fine-grained base (usually feldspathic) through which crystals, as of feldspar or quartz, are disseminated. There are red, purple, and green varieties, which are highly esteemed as marbles.

Porphyry shell (Zo["o]l.), a handsome marine gastropod shell (Oliva porphyria), having a dark red or brown polished surface, marked with light spots, like porphyry.

Source: Webster's Revised Unabridged Dictionary (1913)