after revisionA model to express the degree of exposure of dissimilar inclusive mineral grains in comminuted particles is derived, providing a simple mathematical relationship among the mineral grain size, comminuted particle size and mode of breakage in terms of fracture as follows: F-E(K)=P[K-3 - (K -2)(3)/K-3]+(1 - P)[K-3 - (K - 1)(3)/K-3], K=D/d in which F-E(K) is the probability function for degree of exposure of inclusive mineral grains, K is the relative size modulus of comminuted particle size D to mineral grain size d. P is the fraction of intergranular fracture (the intergranular fracturing factor) and (1 - P), the fraction of transgranular fracture of the breakage mode. This model was demonstrated experimentally to be suitable for ores of two types -magnetite crystal in talc schist and mordenite amygdules in andesite. This model may provide a practical tool to predict the optimum fineness of grind for economic recovery of metallic values by a leaching operation.