Clay is the oldest and most widely used refractory brick manufacturing raw materials are clay minerals, natural refractory clays can be divided into hard clay and soft clay. 
Manufacturing clay brick is clay mineral raw materials. Natural fire clay can be divided into hard clay and soft clay. In refractory manufacturing process, the former majority clinker used after calcination; latter adding water, plastic, easy sintering, and more as the binding agent. China Shandong and other places flint (hard) and Suzhou clay (soft) are world-renowned high-quality refractory clay. Clay minerals are kaolinite (Al2O3 · 2SiO2 · 2H2O), dickite (same composition and kaolinite, but different in lattice constant), montmorillonite (Al2O3 · 4SiO2 · 6H2O), and mica.