Hobbies And Interests
Function
Weathering creates many types of dirt including clay. Sand and silt also come from the weathering of rocks. Air, water and heat work together to erode rocks and create dirt. Dirt of the largest particle size, we call sand. Dirt of the tiniest particle size, we call clay. Silt contains particles that are in-between the size of clay and sand. For the most part, clay is found nearest the surface of the Earth's crust.
Types
Many types of clay exist. The rock from which the weathered particles came determines the chemical makeup of the clay. The type of rock also determines other characteristics, such as the color of the clay, from a white-gray to a red-brown; and the ability of the clay to absorb water. Some clays absorb water, dry out, then easily become wet and dry out again repeatedly. Others do not rehydrate easily once they have become hardened and dry. The latter type degrades soil needed for growing because nutrients and water run off of the hardened soil.
Significance
Too much clay in soil can make it impossible to grow anything in it, no matter what type of clay composition it is. Clay soil may have just slightly more clay than silt or sand. As such, it may still make a suitable growing medium. However as the clay content increases, the likelihood increases that organic materiel such as humus must be added to the soil to make it suitable for growing plants. If too much clay makes up the soil's composition, it may become impossible, even with additives, to create a productive growing medium.
Considerations
Clay particles soak up a great deal of water. For this reason, it is beneficial to the soil content in moderation. Some clay particles swell 100% their normal size when exposed to water. Clay that shrinks when dry but rehydrates when wet provides a suitable growing medium, if the soil contains approximately one-third clay. However, if buildings are built on soil that contains too much clay, structural damage may occur as the soil swells and shrinks repeatedly with precipitation.
Effects
Too much weathering through rain or other forms of precipitation can permanently alter the chemical makeup of the clay in soils, yielding it useless as a growing medium. This often occurs in tropical rain forests when trees are cut down. The trees provide a canopy that filters some of the rainfall to a fine mist. With no trees, rainfall pours down much harder. This in turn creates runoff rather than absorption. The clay breaks down and loses its chemical composition. The soil that is left contains a degraded clay material that bakes in the warm tropic sun and hardens to a useless, brick-hard dirt.