The abnormal particle size distribution in comminuted heterogeneous ores, caused due the detachment breakage of target miner al grains has been illustrated experimentally for two ore samples. The detachment can be expressed in terms of the factors such as degree of intergranular fracturing and ＇the ratio of loosening down (q)＇ of exposed grains. These factors, which govern the particle size distribution, depend on ore characteristics and comminution equipment. Pyrite grains in mica-chlorite schist have been observed to possess a high inclination toward intergranular fracturing (p = 100%), moderate loosening down ratio in crusher (q = 30%) and a high loosening down ratio in the tumbling machine (q = 60%). The abnormality in the particle size distribution resulting from liberation of pyrite grains is unclear in the corresponding curves since the pyrite grains have only accounted for about 4% by weight in these ore samples. Iron ore fr om Newfoundland has been observed to have moderate high intergranular fracturing (p = 44-52%) and moderate loosening down ratio of the exposed grains (q = 20%, 30%) in jaw crushing and roll crushing operation. This results in obvious abnormal particle size distribution, for high content of specular hematite. The difference between these two samples, in terms of abnormal distribution, is due to the difference in the contents of the target mineral grains. The calculation performed for these samples can be used to evaluate the function in promotion of liberation by special treatment of the ore prior to comminution.