Mineral Commodity Report 20 - Clays

Clay, as a rock term, describes a soft, loose, earthy material containing particles with an average grain size of less than than 0.004 mm (4 mm) in the Wentworth grain size scale and less than 0.002 mm (2 mm) in most soil investigations. Clay is composed mostly of clay minerals, but may also contain quartz, feldspar, carbonates, ferruginous material, and other non-clay materials. All clays, apart from flint clay, can be made plastic when mixed with a small quantity of water. That is, they can be moulded into various shapes that harden when dried.