manganese nodule

Manganese nodules are pebble-like or stony objects found on the deep seafloor, primarily in the Pacific and South Atlantic oceans. They are composed of layered oxides of manganese and iron, with minor amounts of copper, nickel, and cobalt, making them a potential source of these valuable metals.1

These nodules form very slowly, at a rate of about 1 to 4 millimeters per million years, and are typically found in areas with minimal sedimentation. Their formation is thought to occur through the direct precipitation of manganese from seawater onto available surfaces. Two main theories attempt to explain why nodules are more abundant on the seafloor than buried within it: bottom currents may prevent sediment from covering them, and burrowing organisms might keep them at the surface by moving them around.1

While of potential economic interest for mining, economic factors and concerns about managing underwater mining operations have slowed their development.2