This chapter explains how rocks are formed and discuss different methods of identifying the most common rocks and minerals. All rocks are composed of minerals, which are naturally occurring inorganic substances with a definite composition. Rock-forming minerals are mostly silicates, while the remainder are carbonates, oxides, hydroxides and sulfates. Considering the aforementioned mineral features, it is possible to identify common rock minerals during site investigation. Hardness and cleavage can provide important information about the mineral type. The simplified chart presents a systematic approach that can be used for mineral identification. The rock cycle involves the following processes: when magma approaches the surface, volcanic eruptions occur, forming volcanic rocks. Igneous rocks are formed from magma when it cools and solidifies. Sedimentary rocks are composed of discrete fragments of materials derived from other rocks. Many metamorphic rocks develop a strong directional structure, in which rock properties depend on direction.