The inventive structure involves the provision and use of a rotating, fluted, impeller having sling compartments along a side thereof in which frangible materials are progressively introduced, are subjected to impaction with respect to each other and from which, after a build-up of radial angular velocity of the bodies, are projected forwardly radially outwardly with maximized face against a striker abutment and each other within a side-positioned quadrant zone. Thereafter, the broken-up material bodies are advanced past a somewhat tangentially converging forward, space-restricting end of an adjustment plate which may be one member of a striker abutment assembly, by the impeller into a separating zone or passageway along which a fluid stream is counterflowed with respect to rotation of the impeller and employed to substantially immediately separate out broken-up particulates of a desired size from particles of greater than the desired size, with particles being returned to the impeller compartments and recycled with newly introduced material bodies and with the particulates being carried out of the apparatus by the fluid stream. The shaft of the impeller has a balanced, two-way, supporting, working area isolated, bearing mounting.