Taking into consideration their genesis we may divide rocks into three groups. We may distinguish igneous rocks (they come into being in result of volcanic phenomena, both on the surface and under the surface of the Earth), sedimentary rocks (they come into being in the process of sedimentation, i.e. deposition of fine material in water reservoirs or rarely on the land) and metamorphic rocks (they come into being in result of transformations of already existing rocky formations).
