By its classification, there is an assemblage of knowledge about each soil. The current system of classification was adopted by the Cooperative Soil Survey in 1965 and is broken into six categories. In this system classes of soils are defined in terms of observable and measurable properties. Families established in each subgroup are classified on the basis of the properties important to the growth of plants or properties significant in engineering. Texture, reaction, and permeability are among the properties considered.
Soil texture is the relative proportions of sand, silt, and clay particles in a mass of soil.
If the soil particles are greater than 2 mm they are not part of the soil texture and are considered gravel. The amount and kind of clay in a soil, influences the extent to which the soil shrinks as it dries out or swells as it gets wet. The shrink-swell potential refers to the relative change in volume to be expected of soil material with changes in moisture content. Shrinking and swelling of soils damages building foundations, roads, and other structures in places. Soils having a high shrink-swell potential are the most hazardous.