A portable hard rock crusher unit especially useful for low clearance underground mines. Material to be crushed is horizontally fed to the rotary crusher jaws. A curved convergent material flow-path is employed between the two crusher jaws. The outer member of the crusher is a substantially stationary outer curved concave jaw and its inner jaw member is a cylindrical element mounted to give eccentric motion on a shaft. The inner member may freely rotate on its eccentric or it may also be rotatably driven. Material fed between the inner and outer jaw members of the crusher encounters a progressively narrower opening as it is crushed and moved by the peristaltic pumping action caused by the eccentric motion of the movable inner crusher element acting against the outer stationary jaw.