An alluvial soil is found where a piece of land is covered with loose sediments after a river or brook has flooded it. That sludge is called alluvium. Diamonds can be found in alluvial soil as well as in Kimberlite pipes. In India and on the Namibian coast, diamonds are extracted from alluvial soil. Before the 20th century, most diamonds were found there, as opposed to Kimberlite pipes.