In chemical engineering processes in which solids are produced or handled, the strength of the substance plays a key role. The following presents a comprehensive model for one of these processes, crystallization from suspensions. When crystallization kinetics are determined by the formation of fragments and their subsequent growth, the developed model equations can predict the whole crystallization process in a quantitative manner. The size dependent growth behaviour of fragments is explained by the attrition process itself. The predicted influence of material properties on the fracture behaviour of a great number of crystalline substances as well as the suggested growth function for attrition fragments compare well with experimental results. The model equations can be used to estimate when and how brittle fracture will occur in chemical engineering processes and, more specifically, to scale-up suspension crystallizers,