Boridium

From Memory Alpha, the free Star Trek reference.

Boridium is a substance used in Romulan and Federation technology.

Boridium was used in the construction of a Romulan minefield which Enterprise (NX-01) encountered in 2152. (ENT: "Minefield") In 2154, the Romulans utilized a similar technology in the Romulan drone-ship, which used boridium cells in its power matrix. (ENT: "Babel One")

The Hill People of the Argus Riverregion on Rigel IV use boridium for the blades of a kind of knife they produce; one such weapon was involved in a series of murders on Argelius II in 2267. (TOS: "Wolf in the Fold")

The Romulan prison camp on Carraya IV tracked prisoners' locations by using the energy signatures of boridium pellets implanted beneath the skin. (TNG: "Birthright, Part I")

In 2369, boridium was used in exocomps as a power network. (TNG: "The Quality of Life")