Beach placers are a major source of ilmenite, rutile, monazite, and zircon. They have been extensively mined in India, Australia, Alaska (U.S.), and Brazil. Although there are several different types of placer deposits, the two most economically important are stream and beach placers. Beach placers form on seashores where wave action and shore currents shift materials, the lighter more rapidly than the heavier, thus concentrating them. Among the examples of beach placers are the gold deposits of Nome, Alaska; the zircon sands of Brazil and Australia; the black sands (magnetite) of Oregon and California; and the diamond-bearing marine gravels of Namaqualand, South Africa.