Clay is a type of fine-grained natural soil material containing clay minerals. Clay minerals are hydrous aluminum phyllosilicates that can contain variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. The main groups of clay minerals include kaolinite, montmorillonite-smectite, and illite. Talc, vermiculite, chlorite, and pyrophyllite are sometimes also classified as clay minerals. Clay is particularly defined by its plasticity when wet and its ability to harden when dried or fired.
Clay minerals have a wide variety of applications and are used in numerous industries including in ceramics, civil and process engineering, petroleum discovery, recovery and refining, construction, agriculture, cosmetics and art. The potential uses and applications are closely related to their structure and composition. Clay minerals must be assessed for their chemical, physical and toxicological specifications, such as: purity, particle size, texture, stability, chemical inertia, water content, atoxicity, safety and microbiological purity. Assessing these characteristics is integral to identifying the potential of any clay deposit.
Recently environmental awareness has spurred an increased interest in the use of clay minerals in numerous industries as they cause no harm to the environment after disposal. The ubiquity of clay materials and their relatively low cost ensures that they will continue to be used in the future with research and development continually identifying new applications for use.