eelkõige kivimeile omane kristalliline struktuur, mis tulenevalt kristallide väiksusest ei ole eristatav petromikroskoobi abil (vt petromikroskoop, kristalliline struktuur), a crystalline structure (usually of rock) in which the individual crystals are too small to be recognized under petrographic microscope using polarized light (see: petrographic microscope, crystalline structure)