manganese nodules/cobalt crust

There are round, black lumps found in some areas of the Pacific and Atlantic Ocean floors. They are called manganese nodules, and are a result of metal components in the water that have slowly deposited around stones or shark's teeth, eventually growing into round lumps. They only grow a few millimeters in size per 1 Ma. Aside from manganese, the nodules contain iron, copper, cobalt, and nickel, and are attracting attention as a future mineral resource.