Magnesium (Mg) is a chemical element with atomic number 12 and is classified as an alkaline earth metal. It is silvery-white and very light, with a relative density of 1.74 and a density of 1740 kg/m3. Magnesium is the eighth most abundant element in the Earths crust and the third most plentiful structural metal after aluminum and iron. It is the third most abundant element dissolved in seawater, after sodium and chlorine. Magnesium is prepared by reducing magnesium oxide with silicon or by the electrolysis of molten magnesium chloride. It is the eighth most abundant element in the Earths crust, but does not occur uncombined in nature. It is found in large deposits in minerals such as magnesite and dolomite, and the sea contains trillions of tonnes of magnesium, which is the source of much of the 850,000 tonnes now produced each year. Magnesium is used in pyrotechnics, flares, and photographic flashbulbs, and is frequently alloyed with aluminum, which makes aluminum easier to roll, extrude, and weld.