Diamond is the hardest natural substance on Earth. It scores a perfect 10 on the Mohs hardness scale, which is used to measure the hardness of minerals based on their ability to scratch other materials. Although there are other materials that are harder than diamonds, they are not naturally occurring substances. Lonsdaleite, a substance found in meteorites, is predicted to be even harder than diamond, but its claim of being the hardest substance has yet to be confirmed physically.