Magnesium

Magnesium (Mg) , an alkaline earth metal, is not found naturally as a free element as it is highly reactive and therefore extremely flammable. With an atomic number of 12 and a valance electron count of 2, it is a metallic silverly-white, low density and relatively strong metal that tarnishes and discolours when in contact with oxygen, producing a thin film of magnesium oxide coating. Having only 2 valence electrons, magnesium is a highly reactive, positive ionic metal.  Relatively light in weight, it has a density of 1.738 g/mL.  Due to its high solubility in water, the magnesium ion is one of the most abundant elements dissolved in seawater, and is consequently ideal for extraction through electrolysis.

Magnesium, along with its various alloys have a high corrosion resistance and

boiling/melting temperature (650 °C).  Like its chemically and physically closer companions of potassium, sodium and calcium, magnesium is placed high in the reactivity series, and consequently, pure magnesium metal highly unstable and  thus is able to be aggressively burned in nitrogen, carbon dioxide and water, violently reacting with a characteristically bright white-light. Magnesium also reacts exothermically with most acids, producing magnesium chloride and hydrogen gas.

Due to its unstable and highly reactive nature, magnesium is refined through the process of electrolysis, whereby it is separated and extracted from its ore or solute form. A metallic object which violently reacts in contact with water and acids, magnesium's physical and chemical composition enforce the need for magnesium ores (or seawater solution) to be extracted through electrolysis.

Magnesium cannot be extracted through the process of smelting as it is far too reactive.  Being a metal that is above carbon in the reactivity series, magnesium could be displaced by a much reactive metal (ie. Potassium or sodium), but this process in much dangerous and expensive than electrolysis, and is thus  only used in dire circumstances. Although the process of electrolysis is expensive and consumes an enormous amount of electrical energy within the process, it is the most efficient reliable and thorough means of separation for magnesium, and therefore a desirable means of its extraction.