Kairouseki

Kairouseki is a mineral that is found in the ocean. It emits an energy that is similar to what the sea gives out. That's why the marine uses a kairouseki cage to lock up those with powers of a devil fruit. Anyone with powers of devil fruit will have their power suppressed when they come to contact with the mineral.

Usage of the mineral:

Smoker and crocodile have used it to cage people. Some people used it to make jewellery, as seen in episode 142, Nico Robin had to retract her "hands".