Gallicite

Gallicite was a naturally-occurring, though rare, mineral. When the mineral was located, it was usually found in deposits large enough to be mined extensively. The deposits could produce strong electrical currents when metal objects were held nearby.

There were gallicite deposits in Vulcan's Forge on. T'Pau warned Jonathan Archer about these discharges, demonstrating the electrical discharges by throwing a knife into a gallicite-rich area. 

Gallicite could be used to refit a starship's warp coils. About a kiloton of gallicite was enough to refit the coils of an ship. The USS Voyager found gallicite deposits on a seemingly uninhabited Delta Quadrant planet in 2373. However, the mineral was found in conduits used by the native Sakari, living underground, who relied on the deposits to shield their life signs from the Borg. After the Voyager crew helped the Sakari to improve their camouflage against the Borg, the Sakari provided them with a generous quantity of gallicite, allowing them to refit to their warp coils within a week. 

The Nezu operated gallicite mines on their colony planet. 

Gallizit