Brown diamonds

The majority of natural diamonds are brown in color which makes them less attractive as gemstones. Australian diamonds, which constitute one third of the world production, are especially rich in brown stones. Large amount of scientific research was spent to understand the origin of the brown color. Several causes have been identified, including irradiation treatment, nickel impurities and lattice defects associated with plastic deformation, the latter are considered as the predominant cause, especially in pure diamonds. A high-pressure high-temperature treatment has been designed to heal those lattice defects and convert brown diamonds into yellow or even colorless stones.