Magnesium? volatile? Reacts violently with water? Nope. Maybe steam. Someone is leaving out some significant details.
http://www.webelements.com/webelements/elements/text/Mg/chem.html
Magnesium does not react with water to any significant extent. This is in contrast with calcium, immediately below magnesium in the periodic table, which does react slowly with cold water. Magnesium metal does however react with steam to give magnesium oxide (MgO) (or magnesium hydroxide, Mg(OH)2, with excess steam) and hydrogen gas (H2).
BTW magnesium is expensive and relatively rare.