How Diamonds are Formed

Diamonds are composed of pure carbon. In nature, diamond crystallizes from hot carbon-rich fluids in a process that requires tremendous heat and pressure. These conditions only occur deep underground. Some diamonds formed as deep as 420 miles beneath Earth’s surface.

Concentrations of diamonds great enough to be economically feasible for mining are usually found in Earth’s oldest continental regions, called cratons. Cratons consist of inactive geological areas more than 2 billion years old with thick crust and deep roots extending into the mantle beneath. Scientists have determined the ages of some diamonds by dating mineral impurities trapped within the diamonds, revealing that most cratonic diamonds are ancient, some older than 3 billion years.

Diamond atoms in a crystal are arrayed in a regular repeating pattern and its outward form, reflects this internal order. Crystals tend to cleave, or split, along lines called cleavage planes. In the case of diamond crystals, each carbon atom is bonded to four surrounding carbon atoms.