Rocks are naturally formed aggregations of mineral matter. A mineral is a solid, inorganic, crystalline substance with a definite chemical composition and atomic structure (Klein and Hurlbut 1998). Some rocks may also contain non-mineral materials, such as fossils and glass. Rocks are an essential part of the Earth’s crust. They remain intact in water and cannot be excavated without blasting (West 2010). Rocks are important for design and stability of engineering structures, and classification of rocks provides an adequate means for predicting and communicating their properties. Several classifications of rocks are available, some based on texture and mineral composition and others on origin.