A rock consisting of crystals embedded in a compact dark red or purple groundmass. Like other semiprecious stones (cf. jade, jasper), it has been used as a person's name, including a Greek scholar and philosopher (c.232-c.304) who wrote extensively against Christianity. Suggests Charles Bowen: "John was calling on his personal encyclopedia of odd facts for this one."
Not to be confused with porphyria, a disease so named for bodily discolorations purple in color.
As jocus is Latin for “joke”, the translation is thus "joke of Prophyris.”