The impact grinding behaviour of materials can be characterized by the two breakage parameters f(Mat) and xW(m,min) [Vogel and Peukert, Powder Technol. 129 (2003) 101-110]. These parameters are usually determined by single particle milling tests. The parameters are useful for predicting the selection function and the breakage function and thus enable modelling of impact milling processes. So far, no detailed correlations have been established between the breakage parameters f(Mat) and xW(m,min) In and intrinsic material properties. In this work, we study the correlation between the breakage parameters of pharmaceutical powders and their mechanical properties (hardness, Young's modulus and fracture toughness) that are determined from indentation experiments. It will be shown that f(Mat) and xW(m,min) can be expressed in terms of the brittleness index (defined as the ratio of hardness to fracture toughness H/K-c). This correlation allows the prediction of the breakage probability of a material by using only a small number of crystals. (c) 2008 Elsevier B.V. All rights reserved.