Magnesium carbonate anhydrous; MgCO3; Molar mass 84.3139 g/mol Also known as Magnesite, magnesia alba Magnesium carbonate is an inorganic salt whose main use is jn the production of magnesium oxide. It also has a multitude of uses in industrial processes as diverse as flooring, toothpaste and white coating for film projection screens. As it is hydroscopic it is used as "chalk" to dry the hands of athletes and rock climbers. Added to table salt, it prevents it from clumping up and allows the grains to flow freely. Its food additive number is E504.