Direct determination of intergranular fracture during multiphase particle breakage is a difficult task to achieve. Perhaps the only method of analysis is measurement of interphase area before and after comminution. Conservation of interfacial area after crushing is indicative of transgranular random breakage. On the other hand, if interfacial area is diminished after breakage some degree of preferential grain boundary fracture has occurred. For complete liberation of all grains after crushing the interfacial area goes to zero. Thus the interfacial area criterion is an important metric to assess the significance of preferential grain boundary fracture for different breakage conditions. This study describes the development of procedures for detailed analysis to quantify the extent of preferential grain boundary fracture for different breakage conditions using X-ray microtomography (XMT). The breakage of single multiphase copper ore particles (3 mm cubic particles) by slow compression is examined. Procedures developed for interfacial area measurements are discussed and determination of the extent of grain boundary fracture of multiphase particles for different breakage conditions is presented. For the copper ore studied, it is shown that preferential grain boundary fracture occurs at low energy dissipation rates. (C) 2008 Elsevier Ltd. All rights reserved.