Gallicite is a naturally occuring, though rare, mineral deposit. It can produce strong electrical currents when metal objects are held nearby. There are gallicite deposits in Vulcan's Forge (ENT:"Kir'Shara").
Gallicite can be used to refit a ship'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 planet in 2373. However, the mineral was found be to used in conduits used by the native Sakari, living underground (VOY:"Blood Fever").
- It's not entirely certain the two gallacites were supposed to be the same. In fact, the properties of the deposits in "Kir'Shara" seem to preclude it from being anything useful in a starship. Gallicite may or may not be the same as gallacite.