|Ferromanganese nodules on the seafloor. USGS|
Ferromanganese nodules are found more then a mile beneath the oceans where they are usually found in vast quantities on the abyssal plains. Most of these nodules are about the size of the potato although an occasional nodule may be found this the size of your kitchen table. At other times the modules have combined to make a pavement on the ocean floor. For the most part these nodules are composed of iron and manganese oxide, but they can also contain cobalt, copper, and other elements including gold and other precious metals. How these nodules form is actually poorly understood, but they are found in all the oceans of the world as well as its large lakes.
|Ferromanganese nodules from the Pacific floor.|
Photo by Marsin Zych