The main use of magnesium carbonate is in the production of magnesium oxide by calcination. Magnesite and dolomite minerals are used to produce refractory bricks. MgCO3 is also used in the composition of fireproof floors, fire extinguishers, cosmetics, dust powders and toothpaste. Other applications are as fillers, smoke suppressants in plastics, reinforcing agents in neoprene rubber, drying agents, laxatives for loosening the intestines, and color retention in food. Additionally, high purity magnesium carbonate is used as an antacid and as an additive in table salt to keep it flowing freely. Magnesium carbonate can do this because it is insoluble in water, only dissolves in acids, which makes it bubbly (producing bubbles).
As a food additive, magnesium carbonate is known as E504, whose only known side effect is that it can work as a laxative in high concentrations.
Magnesium carbonate is also used in taxidermy to whiten skulls. This compound can be mixed with hydrogen peroxide to make a paste, which is then applied to the skull to give it a white color.
In addition, magnesium carbonate is used as a white coating for the projection screen.