In mining operations, comminution processes are responsible for most of the energy used during mineral recovery. Low fragmentation efficiency of comminution in the range of 1-2% (Tromans, 2008) occurs due to the quasi-static nature of the process which is typically accompanied by low impact velocities. Accurate estimation of efficiency requires a measurement system to account for fractal parameters such as surface roughness and fracture surface area. Continuum breakage models of single particles fail to estimate the actual stress transformation that affects bulk material during comminution. In order to study comminution in a dynamic regime at higher strain rates than those of conventional equipment, a compressed-air apparatus designed to launch a projectile at velocities as high as 450 m s(-1) has been developed to measure the quantitative nature of high-speed impacts on aggregated rock samples. A method to calculate the energy efficiency is also presented. The results of experiments conducted on three materials suggest the energy efficiency of rock breakage can be improved by two or three times under high velocity impact for the same energy input level. The paper reports an empirical model of impact velocity and energy input and discusses the advantages and limitations of this model. (C) 2011 Elsevier Ltd. All rights reserved.