Polished section of an iron-manganese nodule. We can perfectly observe the polymetallic concentric growths. This rare and historical specimen comes, according to the label that accompanies it, from surveys carried out at a Soviet base located in the Indian Ocean (southeast area), in a trench called "naturalis" about 5000 m deep. Due to the consolidating treatment of the piece and these data, we can say that it is an old specimen from perhaps the middle of the s. XX. The best-known nodules come from North American investigations in the Clarion-Clipperton area, in the Pacific Ocean, to the west of the USA, or those off the coast of Peru. Interesting as a source of Mn, Co, Ni, Cu... Very rare to find on the market.