Diamond is the hardest naturally occurring mineral on the Mohs scale.
Diamond consists of carbon atoms arranged in a rigid three-dimensional crystal lattice. This structure gives it a Mohs hardness of 10, the highest value on the traditional Mohs mineral-hardness scale. Hardness describes resistance to scratching, not resistance to breaking.
Diamonds form deep within Earth, commonly at depths of roughly 150 to 200 kilometres, where high pressure and temperature allow carbon to crystallize. Volcanic eruptions can bring them to the surface in rocks such as kimberlite.
Diamond is not the same as the hardest possible material in every engineering test. Some laboratory-made materials and specialized structures can outperform natural diamond in particular measures. Corundum, the mineral found in ruby and sapphire, ranks 9 on the Mohs scale.