Mud is a liquid or semi-liquid mixture of water and any combination of soil types (loam, silt, and clay). It commonly appears after a rainstorm or near a body of water. Modern muds are used as fertilizers because they contain many nutrients that help plants grow. Muds differ from quicksand in that sand in quicksand is fine enough to flow like water, but mud isn't. In mud, particles are large enough to resist flowing, so the entire mass tends to sink. Quicksand also sinks as more dry land is exposed by erosion or when the water recedes. As it does, more sand becomes exposed to the action of wind and water which further diminishes its density. This may eventually cause it to lose its sinking property completely. Muds are usually composed of clay and water. The amount of clay present determines how thick the mud will be when dry. For example, if you mix one part clay with two parts water and stir it well, you can make a thin paste that will dry hard. If you add more water than necessary, the paste will be thicker when dry. Clay particles bond together when wet which helps them retain their shape even when dry. The type of clay present in the mud affects its color.