Miners in South Africa claim they have found the biggest diamond ever. It's twice the size of the Cullinan, the world's biggest diamond. In photos the diamond looks a bit green and is around twice the size of a mobile phone, but diamond experts aren't sure that it is real. They say that large diamonds aren't normally found in that part of South Africa, and diamonds with a green colour are very, very rare. The Cullinan was cut into 105 stones, the biggest of which -the Great Star of Africa - is now among the British Crown Jewels.