Green color in a diamond is the result of being in contact with radiation. In natural green diamonds this takes millions of years, and usually happens when a forming diamond is exposed to alpha parti- cles in uranium compounds or groundwater.
Famous green diamond
The largest and most famous is the 40.70-carat Dresden Green, which was originally mined near Golconda, India in the 18th century. Diamond dealer Marcus Moses brought it to England to sell to the king, but the monarch declined to buy it, and in 1741 the diamond was sold to Frederick Augustus II. It has been kept in Dresden ever since, except during World War II, when it was moved to Moscow’s Green Vault for safekeeping.