CLAY
WHAT IS CLAY AND HOW IS IT FORMED?
Weathering or alteration of some rocks produces clay which is a very fine-grained, unconsolidated rock. Clay is made up of a group of minerals, of which illite, montmorillonite, kaolinite, and chlorite are the most abundant.
HOW EXTENSIVE ARE CLAY DEPOSITS IN ILLINOIS?
Clay deposits in Illinois consist of Quaternary clays, which were deposited by glaciers, lakes, and winds; and of fireclay, shale, kaolin, and “fuller’s earth,” all of which are bedrock deposits. Quaternary clay, fireclay, and shale resources occur widely in very large quantities; “fuller’s earth” and kaolin deposits are small in relation to other clay resources.
HOW IS ILLINOIS CLAY USED?
Surface clay, shale, and fireclay are used in the manufacture of structural clay products, such as brick, drain tile, and hollow block ([fig. 16]). Fireclay is used for a bonding agent in molding sand, for the making of stoneware vessels, for a plaster on the walls of industrial furnaces, and for making refractory brick. Refractory brick must be able to withstand very high temperatures and is used to line industrial furnaces, boilers, kilns, and ladles for molten steel.
Shale and clay are ground up and mixed with limestone in the manufacture of cement. Crucibles, refractories, china, and porcelain are made from kaolin. “Fuller’s earth” is used as a sweeping compound and as an animal litter.
Figure 16—Typical Illinois bee-hive kiln.