Produced jointly by the Minerals Council of Australia and AGSO Magnesium is the lightest of all metals, being about two-thirds lighter than aluminium. Magnesium is too reactive to occur in nature as an element, but its compounds are common. At 2.5 per cent, 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 per cent magnesium by weight. When pure, magnesite contains 47.8 per cent magnesium oxide and 52.2 per cent carbon dioxide.
Magnesite colour varies from white, when pure, to yellowish or grey white and brown.
Hardness is 3.5 to 4.5 and the specific gravity varies from 3 to 3.2. A vitreous lustre and very slow reaction with cold acids distinguishes magnesite from other carbonates. Magnesite, dolomite, sea water and lake brines are used as sources of magnesium metal with the most common source being lake brines and sea water. The resultant magnesite may be very pure. Sedimentary deposits usually occur as thin layers of variable magnesite quality.