Which gemstone is the hardest?

Diamond is the hardest naturally occurring gemstone and mineral, earning the top score of 10 on the Mohs scale, which ranks minerals by their resistance to scratching. This extreme hardness comes from its structure, in which carbon atoms are bonded in a rigid three-dimensional lattice. Because of this, diamonds can scratch almost any other material and are widely used in cutting and grinding tools as well as jewellery. Hardness is not the same as toughness, though; a diamond can still be chipped or split along certain planes. Some laboratory-made materials rival or exceed diamond in hardness.