The five elements of the word Yan belong to earth, because Yan means rock.
Rock is a naturally produced mineral or glass aggregate with a stable appearance, which is combined in a certain way. It is the material basis that constitutes the earth's crust and upper mantle. According to their origin, they are divided into igneous rocks, sedimentary rocks and metamorphic rocks. Among them, igneous rock is a rock formed by the condensation of high-temperature molten magma on the surface or underground. It is also called igneous rock. Magmatic rocks that erupt to the surface are called extrusive rocks or volcanic rocks, while those that condense underground are called intrusive rocks. Sedimentary rocks are rocks formed under surface conditions by the products of weathering, biology and volcanism, which are transported, deposited and diagenetically consolidated by external forces such as water, air and glaciers; metamorphic rocks are formed from pre-formed magmatic rocks, sedimentary rocks or Metamorphic rock is a rock formed by metamorphism due to changes in the geological environment in which it is located.
The deep crust and the upper part of the upper mantle are mainly composed of igneous and metamorphic rocks. Igneous rocks account for about 95% of the area within 16 kilometers from the surface, sedimentary rocks account for less than 5%, and metamorphic rocks are the least, less than 1%. The surface of the earth's crust is dominated by sedimentary rocks, which account for about 75% of the continental area, and the ocean floor is almost entirely covered by sediments. Petrology mainly studies the material composition, structure, structure, classification and naming, formation conditions, distribution rules, origin, mineralization relationship and evolution process of rocks of rocks. It is an important basic subject in geological science.