Polyferranide was a mineral found in deposits, sometimes nearly pure. It was used to seal the warp coils 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 Delta Quadrant moon, though they were contaminated with astilines. They later found pure deposits on the planet of the Sky Spirits. The Sky Spirits gave them some polyferranide, but didn't allow them to mine all that they needed. (VOY: "Tattoo")