We present a new method to implement realistic grain fracture in 3D numerical simulations of granular shear. We use a particle based model that includes breakable bonds between individual particles allowing the simulation of fracture of large aggregate grains during shear. Grain fracture simulations produce a comminuted granular material that is texturally comparable to natural and laboratory produced fault gouge. Our model is initially characterized by monodisperse large aggregate grains and gradually evolves toward a fractal distribution of grain sizes with accumulated strain. Comminution rate and survival of large grains is sensitive to applied normal stress. The fractal dimension of the resultant grain size distributions (2.3 ¿ 0.3 and 2.9 ¿ 0.5) agree well with observations of natural gouges and theoretical results that predict a fractal dimension of 2.58.