Polyferranide

From Memory Alpha, the free Star Trek reference.

Polyferranide is a mineral found in deposits, sometimes nearly pure. It is used to seal the warp nacelles of Federation starships such as the Intrepid-class to prevent them from burning out.

In 2372, the USS Voyager crew detected deposits of polyferranide on a moon, though they were contaminated with acelytes. They later found pure deposits on the planet of the Sky Spirits. The Sky Spirits eventually allowed them to mine some of the polyferranide, but not all that they needed. (VOY: "Tattoo")

Later that year, Voyager away teams scouted the moons of Drayan II and found them rich in polyferranide. Captain Kathryn Janeway attempted to negotiate with First Prelate Alcia of the Drayans for mining access, but she was rebuffed. (VOY: "Innocence")