Alluvial refers to the diamonds that are found in the rivers. It is about rich soil and deposited alluvial material. This process can take place in river areas, river deltas and flood plains. A river is alluvial when erosion is possible due the fact the river flows over its own deposits. This term thus refers to diamonds found in such places in rivers. Alluvial deposits actually contain most of the world’s supply of tin ore, as well as, in some regions, gold, platinum, and gemstones.