Celestial Uranium

Celestial Uranium is one of the seven prismatic ores of YGGDRASIL.

Description
Celestial Uranium is a critical element for the Caloric Stone. In the past, Ainz Ooal Gown discovered through a stroke of luck that by gathering vast quantities of this prismatic ore and then expending it, they could earn the World Item Caloric Stone. Presumably, this metal was found in the Seven Hidden Mines.

Trivia

 * Although Punitto Moe believes that could there be more, the mine discovered by Ainz Ooal Gown was, apparently, the first mine of Celestial Uranium discovered on the game.