Existing theories of fracture and comminution of rock were examined and applied to an idealized blasting configuration to obtain the resulting particle size distribution. The results were reasonable, but more development is required for practical applications. An exploding wire apparatus was developed to generate tensile fracture data in thickwalled cylinders of Westerly granite. The experimental results were interpreted with the aid of a finite-difference continuum mechanics computer program. It is indicated that fracture initiation in Westerly granite requires more than 600 bar hoop tension, but that crack propagation is possible with less.