Infrastructure and Construction Materials Guide — Structural Clay Minerals

Commodity Description

Common clay is the primary clay material used in structural products. It is the most widely used form of clay compared to ball clay, bentonite, fire clay, Fuller’s Earth, and kaolin. Common clay is a fine-grained hydrous aluminum silicate material (for example kaolinite is 2SiO2·Al2O3·2H2O). Typically, common clay is yellow, red or bluish/gray in color.

Geology and Mineralogy

Clay is a layered silicate formed by weathering of other silicate minerals. To develop a clay mineral water is essential. Structurally common clay is composed of planes of cations (positive ions), organized in sheets. Since water is required to form clay minerals, it is rare in the solar system, but is fairly common on Earth where water interacts with other minerals and organic matter to form this material.

Production and Pricing

Based on Mine Safety and Health Administration (MSHA) reporting data there were 69 active common clay operations and an additional 30 mines that operated on an intermittent basis in 2022. Historically common clay has been mined in every state except Alaska, Connecticut, Delaware, New Jersey, and Vermont.

For U.S. production statistics and sale prices, “Clays,” go to p. 60 of the USGS Commodity Summaries 2024.

For World Mine Production and Reserves, “Clays,” go to p. 61 of the USGS Commodity Summaries 2024.

Reserves

Although USGS does report US and global reserves for several clay minerals including bentonite, Fuller’s Earth, and kaolin, they do not estimate total clay reserves. Concurrently, USGS does indicate reserves of common clay are “extremely large.”

Uses

Bricks
The major use of common clay in structural products is bricks. This is one of the oldest building materials used in construction. Bricks are made from common clay mixed with water. The material is then molded, dried, and fired in a kiln to produce a finished product.

Other Uses

• Another application for common clay is as a liner/moisture barrier material in ponds and industrial sites.
• Common clay is also used in construction materials such as sewer pipe.
• Kaolinite is a clay mineral with the chemical composition Al2Si2O5(OH)4. It is an important industrial mineral used in paper and plastic manufacturing

Mining Methods

A large majority of common clay mined in the United States uses surface mining methods. There is a layer of material above the clay material which is known as overburden. The overburden material, typically soil, is removed using shovels and scraper machines. Common clay is very soft and therefore seldom requires drilling and blasting to loosen the material. Normally common clay is removed using a shovel and loaded onto trucks for transportation to processing plants.

Mineral Processing

Common clay is typically processed in a clay shredder. The equipment consists of a hopper (bin) with knives that separate the clay. Frequently, common clay is also processed in a pug mill for bricks.  A pug mill mixes the clay with water producing a semi-liquid material that can be molded into bricks.

Environmental Factors

Common clay, as with most industrial minerals, can expose workers to dust. Therefore, both MSHA and OSHA require workers to use face masks when handling the material.  When pits are closed because of resource depletion, site remediation follows well-established procedures.

References

Mine Injury and Worktime, Quarterly U.S. Department of Labor Julie A. Su, Acting Secretary of Labor Mine Safety and Health Administration Christopher J. Williamson, Assistant Secretary Program Evaluation and Information Resources Office of Program Policy Evaluation January – September 2023 Preliminary.

United States Geological Survey (USGS) Commodity Summaries 2023. https://pubs.usgs.gov/publication/mcs2023. The 2023 summary reports 2022 statistics.

United States Geological Survey (USGS) Commodity Summaries 2024. https://pubs.usgs.gov/publication/mcs2024. The 2024 summary reports 2023 statistics.

U.S. Bureau of Mines Dictionary of Mining, Mineral, and Related Terms. Thrush, Paul W., Editor: United States. 1968. Washington, U.S. Bureau of Mines; for sale by the Superintendent of Documents, U.S. Govt. Printing Office.