Which feature consists of rounded masses of metal oxides and hydroxides commonly found on the deep-sea floor?

• A. Nodule
• B. Radiolarian
• C. Oolite Sands
• D. Sand

Answer: (A)

Rounded masses of metal oxides and hydroxides on the deep-sea floor are nodules, specifically manganese nodules. They form as metal ions precipitate from seawater and accumulate around a small nucleus, growing very slowly into hard, rounded lumps over long times. These nodules are common on abyssal plains and along some mid-ocean ridges, and they can be rich in manganese, iron, nickel, and cobalt. This distinguishes them from radiolarians, which are microscopic silica skeletons of protozoa; from oolite sands, which are warm shallow-water carbonate grains with concentric layers; and from ordinary sand, which is loose sediment lacking the consolidated, metal-rich composition of nodules.