Magnesium is a strong, silvery-white, lightweight metal. It tarnishes mildly when exposed to air. However, unlike other alkali metals, an oxygen-free environment is not necessary for its storage, because it is protected by a thin surface layer of oxide which is impermeable and difficult to remove.
The metal is extracted mainly by the electrolysis of magnesium salts obtained from brine. Although rarely seen in its free state, Magnesium metal is quite reactive and flammable, and burns with a characteristic brilliant-white light. The metal is easy to ignite when powdered or shaved into strips, but is difficult to ignite in mass or bulk. Once ignited, it is difficult to extinguish however, being able to burn in nitrogen, carbon dioxide and water. This property was used in incendiary weapons in the firebombing of cities in World War II.
More positively, magnesium has for long been a useful ingredient in flares. On burning in air, it produces a bright-white light which includes strong ultraviolet. Therefore, magnesium powder (or flash powder) was used as a source of illumination in the early days of photography. Magnesium powder continues to be used in the manufacture of fireworks and marine flares where a brilliant white light is required.
More commercially, the chief use for Magnesium is as an alloying agent, particularly to make Aluminum-magnesium alloys. Since magnesium is less dense than aluminum (two thirds of its density), these alloys are prized for their relative lightness and strength.
Other applications of magnesium include its use as a de-oxidizer for copper, brass and nickel alloys. Magnesium-based strong, light alloys are used in the aircraft and automobile industries, such as in engine assemblies. Alloys of Magnesium with zirconium and thorium have been investigated for their use in aircraft manufacture as well.