English: Zirconium is a hard, silvery grey metal. It is quite reactive, but forms a protective oxide layer in air, which makes it corrosion-resistant. Above all, it is used for special alloys. From cubic zirconia, ZrO2, artificial gemstones can be made, which look very similar to diamonds. After being exposed to air for more than a year, the surface is slightly oxidized and therefore darker and less glossy.