This work examines the main influence factors on the breakage behaviour of pharmaceutical substances and other organic crystals. Particle surface characterisation is done via Atomic Force Microscopy, thus examining the transport properties of the powders. The breakage behaviour is characterised by single particle impact experiments. Mechanical properties are determined by indentation. The results show a clear correlation between the breakage behaviour -- expressed by the breakage probability and the breakage function -- and the hardness and fracture toughness of the material. This allows an estimate about the breakage behaviour of a substance from indentation experiments with far less material consumption than in conventional milling experiments.