A white compound, MgCO3, existing in anhydrous and hydrated forms. The anhydrous material (trigonal; r.d. 2.96) is found in the mineral magnesite. There is also a trihydrate, MgCO3.3H2O (rhombic; r.d. 1.85), which occurs naturally as nesquehonite, and a pentahydrate, MgCO3.5H2O (monoclinic; r.d. 1.73), which occurs as lansfordite. Magnesium carbonate also occurs in the mixed salt dolomite (CaCO3.MgCO3) and as basic magnesium carbonate in the two minerals artinite (MgCO3.Mg(OH)2.3H2O) and hydromagnesite (3MgCO3.Mg(OH)2.3H2O). The anhydrous salt can be formed by heating magnesium oxide in a stream of carbon dioxide:MgO(s)+CO2(g) → MgCO3(s)Above 350°C, the reverse reaction predominates and the carbonate decomposes. Magnesium carbonate is used in making magnesium oxide and is a drying agent (e.g. in table salt). It is also used as a medical antacid and laxative (the basic carbonate is used) and is a component of certain inks and glasses.
MgO(s)+CO2(g) → MgCO3(s)
Subjects: Chemistry — Clinical Pharmacology and Therapeutics.