Diamonds are made of carbon in its crystalline lattice form. In their purest state, diamonds are all colorless, so called “white”. However, during their formation, microscopic amounts of gaseous or other compounds, called inclusions, can become trapped within the developing diamond lattice. The inclusions absorb, scatter and reflect light as it passes through the polished gemstone. This gives the diamond a color. The exact color depends on the concentration and chemical properties of the inclusion.
The wide range of potential inclusions means that diamonds are naturally found in a broader spectrum of colors than any other gemstone. In fact over 300 natural diamond hues have been found. Colored diamonds account for only a fraction of all diamonds mined, making colored diamonds very rare. However, black diamonds are the rarest of all. Typically found in Brazil and the Central African Republic, their black color comes from microscopically included graphite, sulfides, hematite or magnetite, all of which cloud the gemstone as it forms, and give it its metallic black coloration.
Under natural conditions, diamonds form hundreds of miles beneath the Earth’s surface, where the exceptionally high temperatures and pressures cause elemental carbon to undergo a transformation into a crystalline diamond lattice. Volcanic eruptions then transport the diamonds to the Earth’s surface. Originally black diamonds were thought to form in exactly the same way as white diamonds even though they are known to be considerably older. However, this is now another explanation.