Although rare in nature (it’s named for the only known occurrence of it on the Scottish Isle of Mull), mullite is ubiquitous in ceramics. When clay is fired above 1100º C, a network of interlaced mullite needles forms, creating the strong internal scaffolding of stoneware and porcelain. Mullite grogs are made by calcining an aluminosilicate such as kyanite.

For more information on mullite, see the Digitalfire.com Reference Library of ceramic materials.