Magnesium (Mg) is the lightest of all metals, being about two-thirds lighter than aluminium. Magnesium is non-toxic, non-magnetic, has high-impact strength and is resistant to denting. Magnesium is too reactive to occur in nature as an element, but its compounds are common. At 2.5%, magnesium is the eighth most abundant element in the earth's crust. It is the third most abundant element in sea water which averages about 0.13% magnesium by weight.