Glass ceramics and methods of making such

A glass ceramic material comprising zirconium dioxide crystals embedded in an amorphous silicon dioxide matrix and at least one hardness enhancing additive, wherein the zirconium dioxide crystals form cores and the cores are at least partly surrounded by rims, wherein the rims comprise an intergranular phase, and wherein the intergranular phase comprises at least silicon dioxide, zirconium dioxide and at least one hardness-enhancing additive, and wherein the concentration in weight percent of the hardness-enhancing additive is higher in the rims than in the amorphous silica matrix and in the cores.