from
The Collaborative International Dictionary of English v.0.48
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.
[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]