Deuridium
Deuridium was a rare element used by the Kobliad.

The Kobliad were a dying race and used deuridium supplied to them by the Federation to prolong their lifespans by replenishing their  structures.

In 2369, the Federation freighter Norkova was transporting a shipment of deuridium to Deep Space 9 from the Gamma Quadrant en route to the Kobliad homeworld. After exiting the wormhole, Rao Vantika (in the body of Doctor Bashir) took control of the Norkova and tried to steal the shipment but was stopped when Doctor Bashir's mind was able to regain dominance of his body. 

Free deuridium posed a potential hazard to those exposed. Benjamin Sisko considered that if Norkova was destroyed and deuridium was released in the Bajoran system, every populated area would have to be evacuated. ()

de:Deuridium
Elements