The crushing energy in mineral processing industry is usually determined by empirical Bond's index, regardless of the mechanical properties of a rock. Although several attempts have been made to obtain the comminution energy based on theoretical approaches, it would be appropriate to examine this relation based on physical concept. In this study, with the purpose of correlating the strain energy of a rock to the corresponding energy estimated by Bond's index, spherical and cubic shape specimens have been simulated during crushing process between two rigid jaws. The specimens are modeled as elasto-plastic medium considering Mohr-Coulomb failure criterion. To verify the obtained results, finite difference method is used to model the fracture behavior in four volcanic rocks. All possible stages that may occur in the processing zone of crushing cubic and spherical rocks are examined and the combination of crushing stages with the lowest and highest strain energies is calculated based on simulation using FLAC3D code. The obtained strain energies are in good agreement with those of Bond's energy. During the size reduction process of hard volcanic rocks, although shear and tensile fracture occur simultaneously, the shear mode of fracture consumes a larger portion of the crushing energy. (C) 2007 Elsevier Ltd. All rights reserved.