Rocks are the basic components of the crust and the most important constituents of the earth’s lithosphere. According to its formation ways, rocks comprises three categories: igneous rocks (magmatic rocks), sedimentary rocks and metamorphic rocks, which are the products of magmatism, exogenic geological process and metamorphism, respectively. The three rock categories may be interconverted to each other due to the changes of geological conditions, i.e., any rock category can be converted to another rock category.