Grades of Soil

Fine Gravel -- Grade 1

• Fine gravel is between 1 and 2 mm in diameter. Fine gravel's lack of ability to absorb moisture makes plant growth sparse or nonexistent. This grade is primarily used as a construction component in manufacturing concrete and other poured stone treatments. There are many varieties of gravel and it can be classified as a building block to many ore deposits, as it is even found when panning for gold and other precious metals.

Sand -- Grades 2 through 5

• Sand is granular material composed of finely divided rock and mineral particles. It varies in composition depending on the rock sources and conditions of the area where it is found. Bright white sands found in tropical locales comes from eroded limestone deposits and may contain coral shell fragments, while the white sands in some southeastern parts of Europe contain quartz. Uses for sand range from farming for certain crops such as peanuts and watermelons to making glass and sandblasting. Water filtration systems use sand as part of the filtering process, and sand is also used in the manufacturing of concrete and mortar, making sand a vital construction ingredient. Sand makes up soil grades 2 through 5. Coarse sand measures between 1 and 0.5 mm in diameter, medium sand measures between 0.5 and 0.25 mm, and fine sand measures between 0.25 and 0.1 mm. Very fine sand measures between 0.1 and 0.05 mm in diameter.

Silt -- Grade 6

• Silt measures between 0.05 and 0.005 mm in diameter. Silt is carried and deposited by a surface water body but may also be found at the bottom of a water body. Like clay, silt is distinguished by plasticity, or the deforming of a material undergoing non-reversible changes of shape in response to applied forces. A factor in the fertility of land around river basins, such as the Nile and the Mississippi, is the silt deposits that have been settled over centuries of flooding and wind storms. However, an excess of silt deposits due to construction activity or slash-and-burn treatments of land can cause silt to become a pollutant. This process, called siltation, can render farmland inert and nonproductive.

Clay -- Grade 7

• Clay measures 0.005 mm or less in diameter. It is a naturally forming aluminum silicate known for its extreme plasticity and malleability. When dried or heated, it hardens. The distinction between silt and clay varies by method, but the plasticity of clay is higher and it is impermeable to water. Clay deposits are typically associated with large lakes and marine deposits. Uses of clay include ceramic work, construction materials such as adobe, paper making and as natural seals for the cores of dams. Research studies are being conducted to gauge clay's effectiveness to remove heavy-metal deposits from polluted air and water through filtration.