Clays

Abstract The article contains sections titled: 1. Introduction 2. Structure and Composition of Clay Minerals 3. Geology and Occurrence of Major Clay Deposits 3.1. Kaolin 3.2. Smectite 3.3. Palygorskite and Sepiolite 3.4. Miscellaneous Clays 4. Mining and Processing 4.1. Kaolin 4.1.1. Dry Process 4.1.2. Wet Process 4.1.3. Combined Dry and Wet Processing 4.1.4. Special Processes 4.2. Smectite 4.3. Palygorskite and Sepiolite 5. Properties and Uses 5.1. Kaolin 5.1.1. Physical Properties 5.1.2. Paper 5.1.3. Paint 5.1.4. Ceramics 5.1.5. Rubber 5.1.6. Plastics 5.1.7. Ink 5.1.8. Catalysts 5.1.9. Fiberglass 5.2. Smectite 5.3. Palygorskite and Sepiolites 6. Environmental Aspects 7. Production and Consumption Clays are important industrial minerals that are utilized around the world. The clay minerals and materials discussed here are kaolins, smectites, palygorskite and sepiolite, and miscellaneous or common clays. Kaolin is both a rock term and a group minerals name for kaolinite, dickite, nacrite, and halloysite. Bentonite is a rock term and the dominant minerals in bentonite are smectites, which is a group mineral name. Important minerals in the smectite group are sodium, calcium, magnesium, iron, and lithium montmorillonites. Miscellaneous or common clays include shales, mudstones, soil clays, lacustrine clays, glacial tills, and so on, which are used for making brick, tile, other structural clay products, and stoneware pottery. They are usually comprised of a mixture of clay and nonclay minerals, the most common of which are illite, chlorite, mixed‐layer clays, and quartz. The geology and location of clay deposits that are marketed regionally and worldwide are described. Structure, composition, and chemical and physical properties of the clay minerals are discussed. These control the many industrial applications of clay minerals and materials. Important applications are described. World production figures of the various clays are given as of 2004. A brief discussion on health‐related and environmental issues is included.