The hardest natural substance known is diamond. Diamonds are formed under extreme pressure and temperature deep within the Earth's mantle over millions of years. This unique formation process gives diamonds their exceptional hardness, measured on the Mohs scale as a 10, the highest grade. Due to their durability, diamonds are not only used in jewelry but also in industrial applications for cutting, grinding, and drilling. Diamonds are celebrated not only for their unrivaled hardness but also for their brilliance and beauty. As a result, they hold significant value both economically and culturally, symbolizing luxury and commitment in many societies.