Simulating comminution processes is one of the most complex tasks in mineral processing research and the Discrete Element Method seems to be a promising approach. However, the actual comminution processes at grain size level are comparatively challenging to model but essential to other parameters like mineral liberation. Simulations at this scale have to be validated properly, but existing comminution tests do usually focus on integral results for the whole rock sample. In order to fill this gap, test work has to break new ground. Therefore, in a new test, thin-notched rock plates prepared of granite rock were stressed with a chisel under slowly raised compressive load while the force displacement behavior was continuously measured. Each step of spontaneous crack propagation was monitored by a high-speed camera. Following, the actual crack path, its propagation behavior, and the energy input were evaluated to improve the validating quality of grain size level DEM simulations.