IntroductionMany rocks exposed at Earth’s surface show well-defined fabric elements in the form of bedding, stratification, layering, foliation, fissuring and jointing. In general these rocks are inherently anisotropic as their physical, dynamic, thermal, mechanical and hydraulic properties vary with direction (Chen et al. 1998). Experimental results have shown that several types of rocks, such as metamorphic and sedimentary rocks, have inherent or structural anisotropy (Saeidi et al. 2013; Hoek 1964; McLamore and Gray 1967; Horino and Ellickson 1970; Kwasniewski 1993; Nasseri et al. 2003; Al-Harthi 1998). Sedimentary rocks can be isotropic or anisotropic depending on the spacing of bedding planes or lamination developed during deposition. Metamorphic rocks are mostly anisotropic because of the effects of both schistosity and cleavage (Singh et al. 1989; Ramamurthy 1993). The effect of the orientation of schistosity on the Brazilian tensile strength (BTS) of different metamorphic rocks
