In Quake II, Steedium is a light blue crystal that is found in the deepest recesses of the planet Stroggos. It is mined by the Strogg and used as an energy source.
In the higher levels of the mine, Steedium is found as traces in the walls, yet the Lower Mines contain larger formations of the crystal. It also appears to be a component in Strogg rock drilling machines and various laser devices.