In 2016, mining operations in Virginia produced about 292 thousand short tons of common clay and shale with an estimated market value of $3.4 million, and about 394 thousand tons of fuller's earth with an estimated value over $35 million.
Clay is a term used interchangeably to denote a class of very-fine grained sediments, or alternatively a loosely-defined group of hydrous aluminum-silicate minerals. Clay sediments are often characterized by high plasticity, or workability, that is useful for the manufacture of structural clay products such as brick and tile as well as pottery. The term is also applied to the fine-grained earthy material that results from weathering or hydrothermal rock alteration. Shale is a fine-grained sedimentary rock formed by the consolidation of clay, silt or mud.
Clay deposits commonly consist of fine-crystalline or amorphous minerals including kaolinite (Al2Si2O5(OH)4), illite ((H3O,K)y(Al4∙Fe4∙Mg4∙Mg6)(Si8-yAly)O20(OH)4), and montmorillonite, ((Na,Ca)0.3Al2Si4O10(OH)2-nH20). These minerals belong to the clay mineral group distinguished by a layered crystal lattice structure that allows for the exchange of calcium, sodium, potassium, among other ions. This property makes certain clay minerals useful in industrial applications for adsorption, filtration, oil refining, and as additives in paint and paper manufacture.
In Virginia, common clay and shale is mined to produce bricks, cement, lightweight aggregate, and road bed material. Typically sold as a building material or construction aggregate, the market and price are often comparable to other natural aggregates such as sand and gravel. There were 33 active mine operations in 2016. General Shale Brick, Inc., was the largest producer reporting over 100 thousand tons of shale mined at the Roanoke Mine in Botetourt County. In Prince William County, Glen-Gery Corporation reported about 37 thousand tons of shale mined in 2016 to produce brick and other building products.Fuller's Earth
In Virginia the montmorillonite variety of fuller’s earth is produced at two mine operations, one in King and Queen County, the other in King William County. In 2016, approximately 394 thousand tons of fuller’s earth were mined and sold primarily as cat litter. It is also marketed as an oil absorbent floor sweep material and as an animal feed supplement. Extraction of the fuller’s earth is by dragline. These deposits occur in the Tertiary-age Calvert Formation. Due to the more specialized industrial applications of fuller's earth compared to common clay and shale, the market is more competitive and the price substantially higher and typically held confidential by producer companies.
Common clay and shale production and value in Virginia
Gilmer, A. K., Enomoto, C. B., Lovett, J. A., and Spears, D. B., 2005, Mineral and fossil fuel production in Virginia (1999-2003): Virginia Division of Mineral Resources Open-File Report 05-04, 77 p.
Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000.
Willett, J.C., 2017, Stone (Crushed): U.S. Geological Survey Mineral Commodity Summaries 2017, p. 156-157.