The best known precious stone, a clear, colourless crystalline form of pure carbon and the hardest known natural substance. It has a brilliant lustre and can be cut in many ways to enhance the internal reflection and refraction of light to produce a spectacular jewel. Until the 18th century most diamonds came from India and then from Brazil. By the 19th century South Africa dominated the diamond market, with new discoveries in Russia, China, and Australia in the 20th century. Used for adornment since ancient times, the diamond is the main precious stone used in jewellery.