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porphyry

Origin: F. Porphyre, L. Porphyrites, fr. Gr. Like purple, fr. Purple. See Purple.

(Science: geology) 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.

(Science: zoology) Porphyry shell, a handsome marine gastropod shell (oliva porphyria), having a dark red or brown polished surface, marked with light spots, like porphyry.