Manganese nodules are small, round concretions that form on the sea floor, typically composed of iron and manganese oxides surrounding a core of manganese oxide minerals. They range in size from a few millimeters to tens of centimeters in diameter and are found in abundance in the deep ocean, primarily on the abyssal plain.
The formation of manganese nodules is a slow process that takes millions of years, starting with the precipitation of manganese and iron oxides around a nucleus, such as a fossil or a particle of clay or pyrite. Over time, the precipitation continues, gradually building up the nodule layer by layer. The exact mechanisms of formation are not well understood, but it is believed that they are influenced by various environmental factors, such as the concentration of dissolved metals in the ocean water, the presence of microorganisms, and the water currents that circulate nutrients and minerals.