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
Amorphous calcium carbonate to be stable in ambient conditions for up to 3 weeks with most of its porosity retained. Bioavailability: Since 2013 a company named Amorphical Ltd. sells an ACC dietary supplement. Calcium carbonate is being used as a calcium supplement worldwide, however, it is known that its bioavailability is very low, only around 20–30%. ACC is roughly 40% more bioavailable than crystalline calcium carbonate. Drug delivery: Due to the ability to tune the size and morphology of the amorphous calcium carbonate particles (as well as other calcium carbonate particles), they have huge applications in drug delivery systems. Highly porous ACC showed