porphyry,
n. [F.
porphyre, L.
porphyrites, fr. Gr. like purple, fr. purple. See
Purple.].
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. [1913 Webster]
Porphyry shell (Zoöl.), a handsome marine gastropod shell (Oliva porphyria), having a dark red or brown polished surface, marked with light spots, like porphyry.