Manganese nodules are pebbles or stones that are built of onion like layers of manganese and iron oxides.
<em><u>Manganese nodules grow when metal compounds dissolved in water column or in water contained in the sediments are deposited around a nucleus.</u></em>
Most manganese nodules are a product of both diagenetic and hydrogenous growth.
I think the correct answer would be hydrogenous sediment. These sediments are produced when minerals that are dissolved solidify via reaction with water, especially seawater. Other examples are evaporites and oolites. Hope this answers the question.
