“…size, shape, orientation of mineral grains, porosity) on the mechanical behaviour of rock materials have been recognized and studied from several years in different rock types. In particular, the effect of mean grain-size was described in different rock types: limestone (Handin et al, 1957;Fredrich et al, 1990), sandstone (Singh, 1988;Klein et al, 2001;Cheung et al, 2012;Atapour and Mortazavi, 2018), marbles (Olsson, 1974;Wong et al, 1996), anhydrite (Skinner, 1959), dolomite Palchik, 1997, 1998), and igneous rocks (Eberhardt et al, 1999). Generally, it has been observed that larger grains and longer grain boundaries result in longer weakness surfaces.…”