Diamonds are formed in a hundred kilometers deep at high pressures and temperatures. When India first and then Brazil were the largest producers, all the diamonds came from secondary deposits such as river gravels.
Only after the discovery of the diamond rocks kimberlitiche of South Africa in 1870, mining has used systems for processing large amounts of rock.
Today, Australia is the largest producer followed by South Africa, RD Congo, Botswana, Namibia, Russia and Ghana.