Diamond is made of carbon, a chemical element represented by the symbol C on the periodic table. In diamonds, carbon atoms are arranged in a crystal lattice structure, which gives them their incredible hardness and unique optical properties. The formation of diamonds occurs under high-pressure and high-temperature conditions deep within the Earth's mantle over millions of years. Interestingly, the variations in carbon bonding result in different forms of carbon, such as graphite and fullerenes, each with unique characteristics. Diamonds are highly valued for their beauty, leading to their popular use in jewelry.