Diamonds are made of highly organized carbon. Scientists speculate that diamonds originated from carbon dioxide atoms 100 miles below the Earth's surface more than a billion years ago. The carbon dioxide was subject to extreme heat and pressure to form diamonds.
Carbon atoms bond together with four other carbon atoms to create an exceptionally strong bond in the presence of heat and pressure. The strength of this bond gives diamonds their unique hardness. Modern synthetic diamonds are created by subjecting carbon to intense heat and pressure over just a few days in a laboratory. These synthetic diamonds are less pure than natural diamonds, because the carbon used is mixed within a solution containing other elements.