Rhenium is named from the Latin Rhenus, Rhine (river) and was discovered in 1925. Rhenium does not occur free in nature or as a compound in a distinct mineral species. Commercial rhenium is obtained from molybdenite roaster flue dusts obtained from copper-sulfide ores mined in Arizona and Utah. The element is silvery-white with a metallic luster. Rhenium is used as an additive to tungsten and molybdenum based alloys to impart useful properties. It is widely used for filaments for mass spectographs and ion gauges.