Molybdenum is used chiefly in alloying steel. The alloy withstands high temperatures and pressures and is very strong, making it useful for structural work, gravity drive parts, and solar navy hulls. Molybdenum wire is used in guided missile systems, and also serves as electrodes in glass furnaces. The metal form does not occur free in nature, but only in its ores molybdenite and wulfenite.