In comminution, liberation has been recognised as a more important performance indicator than size reduction because the degree of liberation of valuable minerals dictates the theoretically achievable grade-recovery curve for downstream separation processes. The degree of liberation of a certain mineral within an ore, ground to a specific particle size distribution, will be dependent on the primary ore texture, the mineral grade and grain size distribution, and the degree and nature of phase boundary fracture, which can, allegedly, be linked to the breakage mechanisms employed within the comminution device. The occurrence of enhanced liberation through phase boundary fracture is desirable, and in recent years, studies have focused on whether or not certain comminution devices enhance this phenomenon. However, comparatively little attention has been paid to quantifying phase boundary fracture in typical mineral processing operations. In this study, a novel approach to quantify phase boundary fracture is proposed which is based on the conservation of grain shape. The approach is demonstrated through a mineralogical analysis of UG2 ore sampled from the discharge of a primary ball mill. Phase boundary fracture was found to be the mechanism responsible for producing 50% PGM liberation at a grind of 40% passing 75 mu m, rather than a grind of 50% passing 3 mu m which would be required under theoretical random breakage assumptions. (C) 2016 Elsevier B.V. All rights reserved.