Abstract: A hard compact material such as rock is broken by directing a high velocity jet of relatively incompressible fluid, such as water, into a hole which is drilled in the material to be broken. The jet is generated by a nozzle in alignment with the hole and is suddenly arrested in the hole in appropriate position with respect to adjacent free surfaces of the material. A jet stagnation pressure is created in the hole of sufficient magnitude and duration or jet repetion rate to break the material towards the free surfaces. Preferably, a secondary nozzle emits fluid for filling partially or wholly the hole prior to generating the high velocity jet by a primary nozzle.