The fracture and fragmentation of rock grains is attracting increasingly more research attention because it is relevant to today's challenges with particle raw materials. To contribute to understanding the fracture mechanisms of rock grains, the combined finite and discrete element method (FDEM) is adopted to simulate realistically shaped rock grains under single particle axial compression. Two groups of rock grains with different shape characteristics are considered to study their fracture processes under axial compression. Detained information of grain morphology was obtained using computed tomography (CT). The initial microstructure or heterogeneity within each rock grain is represented by a random distribution of the strength threshold. The influences of grain morphology on fragmentation patterns and fragmentation size distributions are systematically investigated. The results reveal that the dominant fracture mechanisms are related to the grain morphology. The more complex the grain shape, the more variable are the fracture patterns deviating from simple vertical splitting. Weibull statistics of grain crushing strength demonstrate that angular grains are characterized by both smaller characteristic strength and smaller Weibull modulus compared to those of rounded grains. This finding suggests that the crushing strength of angular grains may exhibit a more significant size hardening effect. The two-parameter Weibull equation can be used to fit the fragment size distribution, and the knowledge of the two fitting parameters is helpful for assessing the extent of fragmentation. The fragments of both angular and rounded grains satisfy the fractal distribution, and the fractal dimension narrowly distributes around 1.86 +/- 0.16 irrespective of the initial morphology, which is close to the exponent T of the analytical predication of the fragment size distribution results from merged crack branches in three dimensions, where T approximate to 1.67. (C) 2016 Elsevier B.V. All rights reserved.