mullita

Mullite is an aluminosilicate mineral with the chemical formula 3Al2O3·2SiO2. It is best known as a high-temperature phase in aluminous rocks and as a major product of firing in clay-based ceramic bodies. Natural mullite is relatively rare and is typically found in metamorphic environments where aluminous rocks interact with silica at elevated temperatures, often as fine crystals or microcrystalline masses. It is commonly associated with other high-temperature minerals such as sillimanite, cordierite, and corundum.

In geology, mullite forms through metamorphic reactions in aluminous pelites and granulites. Its occurrence in natural rocks is limited in comparison with its widespread synthetic counterpart, which is deliberately produced for industrial use.

Industrial mullite is produced synthetically and is a key component in refractory ceramics. It forms during high-temperature synthesis of alumina and silica and is valued for its high melting point, chemical inertness, and excellent resistance to thermal shock and dimensional instability. Because of these properties, mullite is used in refractory bricks and linings, crucibles, and various ceramic bodies, where it helps maintain strength at elevated temperatures and reduces wear.

In summary, mullite refers to both a rare natural aluminosilicate mineral and, more widely, to a synthetic high-temperature phase essential in modern ceramics and refractory technology. Its combination of hardness, thermal stability, and low thermal expansion underpins its industrial importance.