Lynn Walker, age 11, of Colorado Springs, Colo., for her question:
WHERE IS CLAY FOUND?
A type of expandable clay called bentonite is extremely important in the petroleum industry. It is used to make drilling mud, a material utilized when oil wells are being drilled. Another type of expandable clay is used as a chemical agent during the process of refining oil.
Clay is a substance found in almost every kind of soil. Some soil includes only a small amount of clay while large amounts are found in other soil.
Geologists report that clay is made up of small particles of soil that measure less than four microns in diameter. Here's how you write that number in inches: 0.000157.
Clay also refers to earthy material composed of certain kinds of silicate minerals, especially feldspar, that have been broken down by weathering.
Clay is actually made up of tiny sheet like particles of alumina and silica that are bound together by water. Other minerals give it different colors: iron oxide, for example, can color the clay red while carbon compounds may make it different shades of gray.
Without clay in most soils, agriculture could be in trouble. Clay absorbs ammonia and other gases which are needed for the growth of plants. And clay can also help soil retain the fertilizing substances supplied by manure. Without some clay, soil would not keep its fertility from year to year. Too much clay, however, prevents the movement of air and water through the soil.
There are two types of clay, based on how the substance reacts when mixed with water. Expandable clay swells when water is added and can actually absorb so much water that the clay itself can become liquid. Nonexpandable clay becomes soft but not liquid when mixed with water.
Expandable clay has many uses in the petroleum industry, while nonexpandable clays are used in the ceramics industry for making bricks, pottery, tile and other products.
Pottery makers mold clay into many objects and then place their items in hot ovens called kilns. Heat removes the water from the clay and makes it permanently hard so that in the future it cannot be softened by water.
An almost pure white clay called kaolin is used for making porcelain. In the paper industry, kaolin is also used as a filter that adds whiteness and strength to paper. In addition, a smooth, shiny surface is given to some paper by using kaolin.
Fire clay has a large percentage of silica. Because it can withstand high temperatures, fire clay is used in fireplaces and for making furnace linings.