porphyry \por"phyry\, 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.
   1913 webster

   porphyry shell zool., a handsome marine gastropod shell
      oliva porphyria, having a dark red or brown polished
      surface, marked with light spots, like porphyry.
      1913 webster
see also:
porphyries purple porphyry shell oliva porphyria