The ruby is a red colored gemstone, a variety of the mineral corundum aluminium oxide. The red color is caused mainly by the presence of the element chromium. Its name comes from ruber, Latin for red. Other varieties or colors of gem-quality corundum are called sapphires.
Rubies have a hardness of 9 on the Mohs scale of mineral hardness. Among the natural gems only moissanite and diamond are harder, with diamond having a Mohs hardness of 10 and moissonite falling somewhere in between corundum Ruby and diamond in hardness.