Sarium was a material.
The Starfleet of the mid-22nd century used sarium microcells in powering a variety of their technologies. The Vissians also used sarium microcells to charge their weapons. (ENT: "Cogenitor")
A Vostigye space station destroyed by astral eddies in 2373 was constructed of sarium, boronite, and carbon-60 composites. (VOY: "Real Life")