The invention provides an apparatus for crushing material such as rock and includes a support structure having an inlet and an outlet. A powered rotor shaft rotates with respect to the support structure about a shaft axis, and a rotor mounted eccentrically on shaft describes orbital motion about the shaft axis. The rotor has a rotor wall which moves cyclically and laterally with respect to the axis during the orbital motion. At least one stator is mounted in the support structure to provide a stator wall spaced oppositely from the rotor wall to define therewith opposing walls of a crushing chamber located between the inlet and outlet. Feed direction of material passing between the inlet and outlet is generally perpendicular to the shaft axis, and when the rotor describes the orbital motion, spacing between opposing walls of the chamber varies cyclically. The stator is mounted yieldably so as to move away from the rotor when a pre-determined threshold force is exceeded so as to reduce possible damage. The invention provides a relatively wide crushing ratio and can accept relatively large rocks to reduce them to a relatively fine gravel. The invention generates an essentially continuous crushing action with relatively uniform crushing forces and is dynamically balanced to permit high speed operation to perform "multi-layer" crushing.