Respuesta :
Answer: Poly-metallic nodules
Explanation: Poly-metallic nodules are generally considered to the manganese nodules, formed due to the accumulation of rocks and mineral aggregates at the seafloor, adjacent to the underwater volcanoes.
This nodules appears in concentric layers, i.e these are the layers of manganese hydroxide and iron hydroxide. They are commonly found at the sea floor and have economical importance.
