Coils of magnesium ribbon showing their appearance when fresh (right) and tarnished (left). Magnesium is an alkaline earth metal, with atomic number 12 and symbol Mg. It has a bright, lustrous appearance that dulls in air as it tarnishes with the formation of a layer of magnesium oxide, a process called passivation. When heated in air it burns with a brilliant white flame, a property that has been exploited in its use in flares and flash bulbs.