Mill scale consists primarily of magnetite, Fe3O4, of characteristic bluegray "steely" color. An extremely thin outer film of hematite, Fe2O3, is invisible to the naked eye. The inner portion of the magnetite contains fine metal grains and residual ferrous oxide as wüstite, FeO, typically black colored.
Nonferrous are metals other than iron and alloys that contain little to no iron. Other nonferrous metals include brass, titanium, beryllium, nickel and zinc. Nonferrous metals are used for structural building that requires less weight, more strength, nonmagnetic properties, higher melting points, or resistance to .