Molybdenite is an important ore of molybdenum, and is the most common source of the metal.  While molybdenum is rare in the Earths crust, molybdenite is relatively common and easy to process, and accounts for much of the metals economic viability. Molybdenite is purified by froth flotation, and then oxidized to form soluble molybdate. Reduction of ammonium molybdate yields pure molybdenum metal, which is used for fertilizer, as a catalyst, and in battery electrodes. By far the most common use of molybdenum is as an alloy with iron. Ferromolybdenum is an important component of high strength and corrosion-resistant steel.