The hardest known natural substance is diamond. Formed deep within the Earth's mantle under extreme pressure and high temperature, diamonds are essentially crystalline carbon structures. Their unique arrangement gives diamonds their exceptional hardness, making them resistant to scratching and wear. This property is what makes diamonds highly sought after not only for jewelry but also for industrial applications where cutting or grinding is required. The value of diamonds in jewelry markets is primarily related to their rarity, brilliance, and symbolic significance. Despite their beauty, diamonds are still primarily composed of the same element found in carbon-rich materials, highlighting their remarkable transformations under geological conditions.