Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition {containing SiO2, Al2O3 and a divalent metal oxide as main constituents}
Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition {containing SiO2, Al2O3 and a divalent metal oxide as main constituents}