APHANITE, a name given to certain igneous rocks which are so fine-grained that their component minerals are not de tected by the unaided eye. Although a few authorities still recog nize the aphanites as a distinct class, most systematic petrologists have now discarded it and regard these rocks as merely structural facies of other species. Any rock which is compact, crystalline, and fine grained is frequently said to be aphanitic.