With a few unusual exceptions, the only kind of rock that can bear diamond to its accessible depth is called kimberlite, after the town of Kimberly, South Africa. There are few kimberlite pipes in existence, and not many contain important quantities of diamond. Alluvial diamond sites are called secondary deposits. Massive geological shifts, and the movement of glaciers and water can bear diamonds thousands of miles from their original underground source. Most of the world's finest diamonds were discovered in secondary deposits, in the famous river-bed mines of India.
Diamonds can also travel to marine deposits.
At present, one of the richest of the world's diamond sources is found on a l00-mile stretch of beach south of Namibia. Eons ago these were South African diamonds, carried down-river in dirt and gravel debris toward the Atlantic ocean. The larger diamonds sank into the ocean floor, while others were left at the shoreline by currents and storms. It is thought that Antarctica, with its large cratons, may be a rich potential source of diamonds. However, international accords prohibit mining Antarctica.