A cyclosilicate mineral sometimes used as a gemstone. It has the composition (Mg,Fe)2Al4Si5OH2O. It has an extremely low coefficient of thermal expansion and is therefore made synthetically by baking clays in a furnace for use in catalytic converters (where the cycle of hot and cold do not cause it to fracture).
H2O. It has an extremely low coefficient of thermal expansion and is therefore made synthetically by baking clays in a furnace for use in catalytic converters (where the cycle of hot and cold do not cause it to fracture).