The three basic types of soil are sand, silt and clay. Other soil types include loam, peat and saline soil. Soil is comprised of finely ground rock particles and organic material such as the remains of decomposed plant matter.
People classify soil according to its distinguishing characteristics and the criteria that dictate its potential use. Classification of soil types depends upon the soil's intended purpose. The Unified Soil Classification System is the most common method North American engineers use to determine soil type. Systems such as the U.S. Department of Agriculture soil taxonomy and the World Reference Base for Soil Resources classify soils used as resources.