Clays

South Carolina produced the first kaolin mines in the United States. Today it contains some of the most productive clay beds in the United States, second only to neighboring Georgia. The predominant clay region in South Carolina follows the trend of the Sandhills across the upper coastal plain, with major production centered in Aiken County near the towns of Aiken, Bath, and Langley. Smaller mines are in production in several other counties including Clarendon, Fairfield, Kershaw, Richland, and Lexington.

Clay was first mined for pottery production in southern Edgefield District (later Aiken County), which became a center of pottery making in the state. In England the eighteenth-century china manufacturer Josiah Wedgwood wrote of important kaolin deposits in the colonies, including South Carolina. Before the Revolutionary War, small quantities of South Carolina clay were shipped to England and used in Wedgwood’s pottery factories. In 1848 Michael Tuomey wrote in his report on the geology of South Carolina that there was “porcelain clay or kaolin” at Hamburg, Aiken, and Graniteville.

Today, South Carolina produces clay not for pottery but for industrial uses, including paper manufacture. Because clay particles are so small, inert, and insoluble, they are used to fill in microscopic holes in paper and then to coat the surface, which gives magazine paper a high gloss. South Carolina kaolin is also used as an additive to rubber and fiberglass. In addition, clays are mined for the manufacture of brick products. For many years South Carolina also produced fuller’s earth, a clay that was used as an industrial absorbent.

The clays that formed the deep deposits mined in South Carolina were derived from the weathering and erosion of rocks, many from the high mountains that stood to the north and northwest. These mountains were composed largely of granites, gneisses, schists, and phyllites, all of which contain the minerals feldspar and mica, which over time and with exposure to the elements were altered chemically into clay. Because the quartz in these rocks is stable at the surface and so does not weather quickly, this hard and durable quartz became sand as the rocks disintegrated. Over millions of years streams and rivers carried sand and the fine clay particles to lakes and to the sea, where they were deposited together and differentially, the sand settling nearer the shore and the lighter clay settling further offshore. As the clay settled into the ocean it formed deposits hundreds of feet thick. The ages of the clay mined in South Carolina run from the Cretaceous period to the early and middle Tertiary period. The deposits of Cretaceous clays, called “soft clays,” are much smaller than those of the more abundant Tertiary clays and are used primarily to produce brick. The younger Tertiary clays, called “hard clays,” are used generally for other industrial purposes.

The clay mines of South Carolina are all open-pit. Commonly, one hundred feet of overburden is removed to get to the clay, which currently runs to no higher than eighty percent purity. Mines use small draglines, power shovels, front-end loaders, and hydraulic backhoes to dig the clay. The collected clay then goes through a refining process called beneficiation, through which the clay is dried, pulverized, air floated, collected, and shipped to destinations largely out of state.

An understanding of the geology of South Carolina’s clay deposits, including the ages of the clay beds and the sequence of their depositional history, has been derived partly through the study and interpretation of many types of marine fossils found within them. Signs of many species of both vertebrate and invertebrate animals as well as plants have been found. These have included nannofossils (extremely small marine fossils, usually algae), sharks, rays, barnacles, shells, and burrows. Scientists continue to study the clays of the state both to understand South Carolina’s geology further and to identify new sources of the clays that have provided such great economic benefit.

Murphy, Carolyn H. Carolina Rocks! The Geology of South Carolina. Orangeburg, S.C.: Sandlapper, 1995.

Nystrom, Paul G., Jr., and Ralph H. Willoughby, eds. Geological Investigations Related to the Stratigraphy in the Kaolin Mining District, Aiken County, South Carolina: Carolina Geological Society Fieldtrip Guidebook, October 9–10, 1982. Columbia: South Carolina Geological Survey, 1982.