Ferromanganese nodules form in the oxidizing environment of the abyssal pelagic zone. They are the result of ion exchange reactions that precipitate ore components from the water (sedimentary) or out of the interstitial water of the sediments layers (diagenetic). The composition of Manganese-bearing minerals is dependent on how the nodules are formed; sedimentary nodules, which have a lower Mn2+ content than diagenetic, are dominated by Fe-vernadite, Mn-feroxyhyte, and asbolane-buserite while diagenetic nodules are dominated by buserite I, birnessite, todorokite, and asbolane-buserite.
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