The mineral primarily responsible for the hardness of diamonds is carbon. Diamonds are a crystalline form of carbon where each carbon atom is bonded to four other carbon atoms in a tetrahedral structure. This arrangement gives diamonds their exceptional hardness, making them the hardest known natural material on Earth. The strength of the covalent bonds between the carbon atoms contributes to their durability and brilliance, which is why diamonds are highly prized not only in jewelry but also in industrial applications like cutting and drilling tools. Thus, the unique properties of carbon in its diamond form make it extraordinary.