Cosmoium

From Memory Alpha, the free Star Trek reference

Name:	Cosmoium
Symbol:	Cs
Atomic Number:	Unknown
Atomic Weight:	37

Cosmoium is a chemical element listed on the Table of Elements. (TNG: "Rascals")

The element Cosmoium had the symbol "Cs" which is the same atomic symbol used for Cesium. It is presumably named for the fictional element from John W. Campbell, Jr's. "Invasion of the Infinite." Cosmoium was supposedly composed of solidified light, in the form of exotic cosmic ray photons instead of ordinary light. Its specific gravity was 5007.89 and tensile strength about two hundred thousand times that of steel.