A liberation model extended from Gaudin＇s model by incorporating a detachment factor, in addition to a mineral grain size distribution, is proposed. The experimental application of this simple, physically-realistic model was demonstrated to be suitable for two ore samples: magnetite in talc schist from Hwalian, Taiwan and mordenite in andesite from the northern coastal range of eastern Taiwan. Both of these samples exhibit a high ratio of grain boundary fracture during roller crushing. With data taken from published results, four rock samples including nine mineral-gangue systems may also be correlated by this model. A general increase in the estimated detachment factor with an increased hardness difference is demonstrated, suggesting that the distribution of the average mechanical strength of the mineral, gangue and their interfacial layer is the governing factor in liberation by detachment. Physical properties such as hardness, cleavage, and the mineralogical texture of ores such as crystal form and orientation which affect the tensile strength are considered to be the function of this factor. The quantitative detachment factor can be used to express the possibility of fracture along the grain boundaries during various comminution processes.