Calcium carbonate latter is especially evident in day-to-day life of people who have hard water. Water in aquifers underground can be exposed to levels of CO much higher than atmospheric. As such water percolates through calcium carbonate rock, the CaCO dissolves according to the second trend. When that same water then emerges from the tap, in time it comes into equilibrium with CO levels in the air by outgassing its excess CO. The calcium carbonate becomes less soluble as a result and the excess precipitates as lime scale. This same process is responsible for the formation of stalactites and stalagmites in limestone
Calcium carbonate source of dietary calcium, but are also a practical industrial source. Dark green vegetables such as broccoli and kale contain dietarily significant amounts of calcium carbonate, however, they are not practical as an industrial source. Beyond Earth, strong evidence suggests the presence of calcium carbonate on Mars. Signs of calcium carbonate have been detected at more than one location (notably at Gusev and Huygens craters). This provides some evidence for the past presence of liquid water. Carbonate is found frequently in geologic settings and constitutes an enormous carbon reservoir. Calcium carbonate occurs as aragonite, calcite and dolomite. The carbonate minerals