② Sedimentary rocks. Layered rocks formed by transportation, deposition and diagenesis of weathered materials, pyroclastic materials, organic matter and a small amount of cosmic materials at normal temperature and pressure on the surface. According to the genesis, it can be divided into clastic rocks, clay rocks and chemical rocks (including biochemical rocks). Common sedimentary rocks are sandstone, tuffaceous sandstone, conglomerate, clay rock, shale, limestone, dolomite, siliceous rock, iron ore, phosphorite and so on. Sedimentary rocks occupy 7.9% of the crust volume, but they are widely distributed in the surface layer of the crust, accounting for about 75% of the land area, and the seabed is almost completely covered by sediments. Sedimentary rocks have two prominent characteristics: one is bedding, which is called bedding structure. The interface between layers is called bedding plane, and usually the rocks below are older than the rocks above. Secondly, many sedimentary rocks contain "stony" remains of ancient creatures or traces of their existence and activities-fossils, which are precious materials for judging geological age and studying ancient geographical environment, and are called "pages" and "words" for recording the history of the earth.
③ Metamorphic rocks. Rock formed by metamorphism of original rock. According to the types of metamorphism, metamorphic rocks can be divided into five categories: dynamic metamorphic rocks, contact metamorphic rocks, regional metamorphic rocks, migmatites and metasomatic metamorphic rocks. Common metamorphic rocks include mylonite, cataclastic rock, amphibole, slate, phyllite, schist, gneiss, marble, quartzite, amphibole, schist, eclogite and migmatite. Metamorphic rocks occupy 27.4% of the crust volume.
Rock has specific physical properties such as specific gravity, porosity, compressive strength, tensile strength, etc. It is a factor to be considered in construction, drilling, excavation and other projects, and also a carrier of various mineral resources. Different kinds of rocks contain different minerals. Taking igneous rocks as an example, basic ultrabasic rocks are related to iron-loving elements, such as chromium, nickel, platinum group elements, titanium, vanadium and iron. Acidic rocks are related to ishihara-loving elements, such as tungsten, tin, molybdenum, beryllium, lithium, niobium, tantalum and uranium. Diamond only occurs in kimberlite and K-Mg lamprophyre; Chromite is mostly produced in pure peridotite; The early Yanshanian granite in South China is rich in tungsten-tin deposits. Independent tin deposits and niobium, tantalum and beryllium deposits are often formed in granite in the late Yanshan period. Oil and coal exist only in sedimentary rocks. Iron ore in Precambrian metamorphic rocks is worldwide. Many stones are also important industrial raw materials, such as white marble in Beijing, which is a well-known building decoration material at home and abroad. Rainflower Stone in Nanjing, Shoushan Stone in Fujian and Qingtian Stone in Zhejiang are all good arts and crafts stones, and even river sand and pebbles that are not noticed by people are very useful building materials. Many rocks are also important raw materials of traditional Chinese medicine, such as medical stone (a kind of intermediate-acid dike rock), which is a very popular medicinal rock. Rock is also an important factor in tourism resources. The famous mountains, rivers and grottoes in the world are all related to rocks. Our ancestors have been using rocks since the Stone Age. In today's highly developed science and technology, people can't live without stones without clothing, food, shelter, transportation and medical care. Studying rocks, using rocks, hiding rocks, playing with rocks and loving rocks are no longer the patents of scientists, but gradually become an integral part of the lives of the broad masses. Weathered rocks are broken and loose under the action of solar radiation, atmosphere, water and organisms, and the mineral composition changes secondary. The action leading to the above phenomenon is called weathering. Divided into: ① Physical weathering. It mainly includes the expansion and contraction of rock caused by temperature change, the freezing of water in rock cracks, the expansion caused by salt crystallization and the expansion of rock caused by load release. ② Chemical weathering. Includes: the rock is dissolved by water; Minerals absorb water to form new water-bearing minerals, causing hydration of rock expansion and disintegration; Hydrolysis process in which minerals react with water to decompose into new minerals; Rock oxidation destroyed by free oxygen in air or water. ③ Biological weathering. Including the destruction of rocks by animals and plants, the mechanical destruction of rocks is also physical weathering, and the erosion of rocks by corpse decomposition is also chemical weathering. Man-made destruction is also an important cause of rock weathering. The weathering degree of rocks can be divided into four grades: total weathering, strong weathering, weak weathering and mild weathering. About 200 years ago, people may think that mountains, lakes and deserts are the eternal characteristics of the earth. But now we know that mountains will eventually be weathered and denuded to the ground, lakes will eventually be filled with sediments and vegetation, and deserts will be uncertain with climate change. Matter on the earth moves endlessly. Most rocks exposed to the earth's crust are in different physical and chemical conditions from those when they were formed, and the surface is rich in oxygen, carbon dioxide and water, so rocks are easy to change and destroy. It shows that the whole rock has become fragments, or the composition has changed, and finally the hard rock has become loose debris and soil. The process of mechanical crushing and chemical decomposition of minerals and rocks under surface conditions is called weathering. Due to the dynamic effects of wind, water flow and glaciers, the process of removing the weathered products from their original places is called denudation, and the process of mechanically crushing the surface rocks in situ without changing their chemical composition or new minerals is called physical weathering. Such as thermal expansion and cold contraction of mineral rocks, ice splitting, peeling and salt crystallization. , can make the rock from large to small or even completely broken. Chemical weathering means that the chemical composition and mineral composition of surface rocks change under the action of water, oxygen and carbon dioxide, and new minerals are produced. Mainly through the equations of dissolution, hydration, hydrolysis, carbonation and oxidation. Although all rocks will be weathered, they don't all change along the same road or at the same speed. After years of observation of weathered rocks under different conditions, we know that rock characteristics, climate and topographic conditions are the main factors controlling rock weathering. Different rocks have different mineral compositions and structures, and the solubility of different minerals is also very different. The distribution of joints, bedding and pores and the grain size of minerals determine the brittleness and surface area of rocks. The difference of weathering speed can be seen from the stone tablets of different rock types. For example, granite stone tablets are mainly composed of silicate minerals. This kind of stone tablet can resist chemical weathering well. Marble stone tablets are obviously prone to weathering. Climate factors mainly include temperature, rainfall and biological reproduction. In a warm and humid environment, the temperature is high, the rainfall is heavy, the plants are dense, the microorganisms are active, and the chemical weathering is fast and sufficient. The deep decomposition of rocks can form a thick weathered layer. In polar and desert regions, due to the dry and cold climate and little chemical weathering, rocks are easily broken into angular debris. The most typical example is that the well-preserved Kleopatra granite spire, which has stood in dry Egypt for 35 centuries, was moved to the central park in new york City, where the air pollution is serious. It was 75 years before it was completely unrecognizable. The height of the terrain affects the climate: the temperature and climate of the foothills and tops of high mountains in the middle and low latitudes are very different, and the biological characteristics are significantly different. Therefore, there are significant differences in weathering. The degree of undulation is also of universal significance to weathering: in mountainous areas with large undulations, weathering products are easily eroded by external forces, exposing bedrock and accelerating weathering. The trend of hillside is related to climate and sunshine intensity. For example, the sunny slope of the mountain has strong sunshine and much rain, while the sunny slope of the mountain may not be frozen all year round. Obviously, the weathering characteristics of rocks are quite different. Erosion and weathering complement each other in nature. Only when rocks are weathered can they be easily eroded. When the rock is denuded, fresh rock will be exposed to continue weathering. The transportation of weathering products is the main embodiment of erosion. When cuttings flow with conveying media (such as wind or water), they will erode the surface, river bed and lakeshore zone. In this way, more debris is produced, which provides material conditions for deposition. Under the action of sunlight, moisture, living things and air, rocks are gradually destroyed and decomposed into sand, which is called weathering. Sand and soil are the products of rock weathering.