Refractory clay is a general term for clays that are composed mainly of silicic acid, alumina, and water, and contain some iron and other impurities, and turn yellow when calcined, but have a refractoriness of S.K26 or higher. In terms of composition, there are two types of clays: primary clays associated with residual deposits, such as kaolin, and secondary clays that form drifting deposits, such as wood-section clay and frog-eye clay. However, the constituent minerals are all mainly kaolin minerals. Refractory clays have two types of properties: those that are rich in plasticity and suitable for binding materials, such as wood chips and ball clays, and those that are hard and lumpy, such as Iwate clay and Fushu clay, and are suitable for raw materials of burnt powder.
