Their Importance and Function in Soils by M. Ray Tucker People tend to have a negative opinion of clay soils. It is true that these soils can be difficult to till or spade. Also, they may not drain quickly after heavy rain and often harden when dry. In spite of these drawbacks, however, some of the most productive soils across North Carolina contain significant amounts of clay.
Most soils contain a mixture of clay, organic matter, sand and silt.
Soils of three North Carolina research stations classified by texture. Clay is a naturally occuring, inorganic component of most soils. Clay is made up of tiny particles less than 0.002 mm in diameter. By comparison, silt particles range from 0.002 to 0.05 mm in size and sand particles from 0.05 to 2.0 mm . Because clay particles are so small, pure clay has at least 1000 times more external surface area than coarse sand.