Surface features of uniaxial tensile fractures and their relation to rock anisotropy in Inada granite

Uniaxial tensile fractures parallel to the rift, grain and hardway planes were formed in Inada granite. Most of the fractures split the rock-forming mineral grains as transgranular paths under microscopic observations. The surface topography of the fractures was measured by the stereo-photogrammetric technique, and is different in different orientations. The rift-parallel uniaxial fracture has the smoothest surface, and the grain-parallel fractures are smoother than hardway-parallel fractures. The mineral compositions are also different on the failed surfaces of different directions. The rift-parallel fractures have almost the same constituent mineral ratio as the parent rock. However, the grain-parallel fractures pass preferentially through feldspar grains, and contain less quartz grains as compared to the bulk composition of the parent rock. In addition, it is remarkable on hardway-parallel fractures. It is considered that the differences of surface topography and mineral compositions are caused by preferred orientations and spatial distributions of pre-existing microcracks in Inada granite.