Magnesium carbonate has the molecular formula of MgCO3 and the molecular weight of 84.3145 g/mol.For the most part,Mg2+ forms several hydrated and basic carbonates that are stable and occur in nature.
The calcite structure of magnesium carbonate has the form wherein Mg2+ is surrounded by six O2- atoms. The dihydrate composition has a triclinic structure, while the trihydrate has a monoclinic structure. References to “light” and “heavy” magnesium carbonates actually refer to the magnesium hydroxycarbonates. A space-filling structure of the anhydrous salt is seen in the above diagram where the triangular CO3 2- groups are clearly visible.