They form as rocks are eroded by the forces of weather, both wind and rain.
Much of the sand and silt is small but visible grains of rock. However, some of it can become so fine that it is microscopic, especially when it comes to clay.
Clay is an extremely important part of soil. Because of its porous nature, water is able to seep through clay with ease. Most clays have a negative charge which attract positively charged particles suspended or dissolved in water. As a result, many important chemical reactions take place in clay.
Soils usually contain inorganic material of three sizes: sand, which ranges in diameter from 0.2 to 2 millimetres; silt, between 0.02 and 0.002 millimetres in diameter; and clay, which is less than 0.002 millimetres. Most soils have some of each. Soils with a large proportion of each component are called loams