Calcium carbonate is a naturally occurring chemical compound, with formula CaCO3. It is the residue of marine organism shells, which form limestone, and is used in a broad range of applications, including cement, chalk and agricultural products.
Calcium carbonate is the main chemical component of limestone, calcite, scale (white residue in kettles), aragonite, chalk, marble, pearl, and oyster.
CaCO3 will react with acid, and thermally decompose, to release CO2. This makes it particularly susceptible to acid rain attack.
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
CaCO3(s) + 2H2SO4(aq) → CaSO4(aq) + CO2(g) + H2O(l)
heat + CaCO3 → CaO(s) + CO2(g)
Formation of bicarbonate: CaCO3(s) + CO2(aq) + H2O → Ca(HCO3)2(s)
The bicarbonate reaction occurs when rain water saturated with CO2 erodes limestone rock to form caverns. It also creates hard water.
Evidence of calcium carbonate on Mars may indicate that liquid water was once prevalent on the planet.