Jade is the common name for two minerals used as gemstones: jadeite and nephrite. There is also fake jade in the economic circuit. This one is worth less than real jade. The two can be distinguished by the fact that real jade changes color over a long period of time when it has been in contact with human skin for years. Jade comes in many different colours: green, brown, black or cloud white, from very light to very dark. Like soapstone and chalcedony, jade has been polished and processed by the Chinese for thousands of years. Jade was originally used as a tool but came into fashion as a piece of jewelry during the Han dynasty. The only place where nephrite is found in China is in Sinkiang around the city of Khotan. In Chinese culture, only processed jade is considered valuable. A lump of raw jade is therefore of less value. In the Sanzijing it is mentioned as a comparison with education: "If one does not polish jade, it is not a precious thing. If a man does not learn, his life has no meaning, because he does not know the norms, values and respect of life. and thus will never become talented" (玉不琢 不成器 人不學 不知義). Jade is seen as a precious stone that wards off evil forces. If one wears a piece of jade on one's body for a long time, for example on a piece of red thread around the neck, one will see that the jade slowly changes color. During the 2008 Olympic Games in Beijing, the medals are provided with jade.