The hardest known natural material is diamond. Formed deep within the Earth's mantle under high pressure and temperature conditions, diamonds are composed of carbon atoms arranged in a crystal lattice structure. This unique arrangement gives diamonds their unparalleled hardness, making them highly sought after for industrial applications such as cutting, grinding, and drilling, as well as for use in jewelry. Their brilliance and refractive quality also contribute to their status as a symbol of luxury and wealth, making diamonds a popular choice for engagement rings and other exquisite adornments.