Dikironium
From Star Trek : Freedom's Wiki
Dikironium is an element which, in the mid-23rd century, was not believed to exist in nature until the crew of the USS Enterprise encountered a cloud creature that was composed of that element. (TOS: "Obsession")
It is possible that Kironide, the substance which the Platonians ingested to give themselves telekinetic powers in "Plato's Stepchildren", is related to dikironium.
