The U.S. Bureau of Mines has a long-term program on nonexplosive fragmentation of hard rock. The thrust of this research has been water-jet and mechanical fragmentation. The ultimate objective is to develop equipment and procedures for continuous hardrock extraction as an alternative to the cyclic drill-blast-muck system used in most underground hardrock mines. In the quest for a more continuous mining system, the Bureau has introduced two mechanical systems, the radial-axial splitter and the ripper-miner. Both have been shown to be capable of continuous hardrock fragmentation.