porphyraceous,a. ? Obs.rare.|pɔːfɪˈreɪʃəs| [f. porphyr- + -aceous.] Of the nature of or allied to porphyry; porphyritic. 1799Kirwan Geol.Ess. 207 Charpentier mentions a sort of stone which he calls porphyraceous, though he does not ascribe felspar to it. Hence1828in Webster; and in mod. Dicts.