Pieces of metal made up of a noranium alloy
Noranium is an element used to create alloys.
Noranium vaporizes at 2,314 °C, and noranium carbide at a slightly higher temperature. When heated it releases a vapor which forms clouds of smoke. Burning noranium can be extinguished with sand. A Starfleet type-2 phaser at setting 7 can heat noranium to the vapor point.
Noranium alloys have a very low scrap value, but are still collected by the Gatherers. (TNG: "The Vengeance Factor")