Sedimentary rocks are classified into three main types: clastic, chemical, and organic. Clastic sedimentary rocks, such as sandstone and shale, form from the accumulation of fragments of other rocks and minerals. These fragments are compacted and cemented together over time, creating solid rock layers. Chemical sedimentary rocks, like limestone and rock salt, form from the precipitation of minerals from water. This process often occurs in bodies of water where evaporation leaves behind mineral deposits. Organic sedimentary rocks, such as coal, develop from the accumulation of plant material and other organic matter, which is compacted over millions of years.