Crushed particles of coal, ores or industrial minerals or rocks are comminuted by feeding them through a feeder (14) into a cyclic stream (19, 22, 38, 39, 41) of cryogenic process fluid such as liquid carbon dioxide and conducting the process stream with the entrained mineral particles to a comminuter (17) and through a zone therein of mechanically generated high frequency vibratory energy, preferably ultrasonic. The comminuter (17) may be multistage with means for re-cycling oversize mineral particles and, after leaving the comminuter (17) the process stream (38) is conveyed to a separator (18) for extracting the comminuted particles and re-cycling the cryogenic fluid to the feeder (14). The low temperature of the process stream is maintained by refrigerating means (16) and losses of the fluid are made up by supplementary fluid fed to the stream.