A rare mineral needed to refit a starship's warp coils, which Voyager's crew went looking for on the Sakari colony world in the episode Blood Fever.
Gallicite is a scarce ore that can be used to rebuild worn warp coils. In the Voyager episode Blood Fever, the ship locates a large deposit on a planet that appears to be an abandoned colony, and Torres, Paris and Neelix climb down into the old mine workings to survey it.
The expedition goes badly. Torres has been affected by the pon farr of the Vulcan ensign Vorik, and the survivors of the Sakari colony turn out to be hiding underground from the invaders who devastated their world. Chakotay negotiates for the gallicite by offering help in concealing the settlement better.
The episode ends with the discovery of a Borg corpse in the ruins, the first sign that Voyager is approaching Borg space.