Erosion and weathering transform boulders and even mountains into sediments, such as sand or mud. Dissolution is a form of weathering chemical weathering. With this process, water that is slightly acidic slowly wears away stone. These three processes create the raw materials for new, sedimentary rocks. Classic sedimentary rocks are made up of pieces of pre-existing rocks. Pieces of rock are loosened by weathering, and then transported to some basin or depression where sediment is trapped. If the sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock.