The hardest mineral known to man is diamond. This remarkable mineral is composed of carbon atoms arranged in a crystal lattice structure, which gives it exceptional hardness and strength. Diamonds are rated a 10 on the Mohs scale of mineral hardness, which is the highest rating on this scale. Beyond its hardness, diamond is also valued for its brilliance and high refractive index, making it a popular choice in jewelry. Due to their strength, diamonds have industrial applications as well, particularly in cutting and drilling tools.