Gallicite

Gallicite is a naturally-occurring, though rare, mineral deposit. It can produce strong electrical currents when metal objects are held nearby. There are gallicite deposits in Vulcan's Forge. T'Pau warned Archer and demonstrated to him the electrical discharges by throwing a knife into that area. (ENT: "Kir'Shara")

Gallicite can be used to refit a starship's Warp Coils. About a kiloton of gallicite is enough to refit the coils of an Intrepid Class ship. The USS Voyager found gallicite deposits on a seemingly uninhabited Delta Quadrant planet in 2373. However, the mineral was found be to used in conduits used by the native Sakari, living underground. (VOY: "Blood Fever")

The Nezu operate gallicite mines. (VOY: "Rise")