Natural black diamonds are more uncommon than colorless diamonds, although being less rare than pink fancy colored diamonds or even yellow diamonds. Some may be surprised, though, because they can be less expensive than colorless diamonds. 3-5% of all diamonds are black. Black diamonds can be found in almost any country around the world. They can be part of a mine dump or residue from geological processes. Sometimes black diamonds are called "dark earth" diamonds. They can also be found in meteorites that fall to Earth's surface. There are two types of black diamonds: organic and inorganic. Organic black diamonds are formed when carbon molecules become trapped inside crystals during formation of other gems such as diamonds or coal. Inorganic black diamonds are made up of pure carbon without any other elements present. They can be found in many different forms including graphite, charcoal, and cavities within rocks. In general, inorganic black diamonds are more valuable than organic ones. Organic black diamonds can be heat treated to make them white or brown and increase their value. For example, some African mines that produce white diamonds also produce small amounts of black diamonds. These black diamonds are removed before the mine is closed down to prevent soil contamination. Heating reduces the amount of carbon left over from gemstone formation and makes them more saleable.