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 Caloric Stone, an expendable-type World Item. Presumably, this metal was found in the Seven Hidden Mines.
The substance has various properties. It will turn into Caloric Stone if enough of the ore is gathered. One is able to fuse the ore with a golem, by creating core from it. The result makes a powerful entity that can be looked at by other players as almost a cheating mechanic.
- Although Punitto Moe believes that there could be other sources for finding the ore, the mine discovered by Ainz Ooal Gown was, apparently, the first mine with Celestial Uranium discovered on the game.