Various forms of mullite occur in porcelains. Primary mullite forms from decomposition of pure clay. Secondary mullite forms from reaction of feldspar and clay and feldpar, clay and quartz. Which of these forms is strongly dependent on the extent of mixing of the body raw materials. Additionally, in aluminous porcelains tertiary mullite may precipitate from alumina-rich liquid obtained by dissolution of alumina filler. The size, shape and composition of the mullite crystals is controlled by the fluidity of the local liquid matrix from which they precipitate and grow, which itself is largely determined by the extent of mixing of the original powder batch.