How do cave stalactites and stalagmites form?

Calcium carbonate (CaCO3), which is insoluble in water, in acid medium H2CO3 forms calcium bicarbonate (CaHCO3) which is water soluble.

The formation of the stalactites, which are in the ceiling of the caves, or the stalagmites, which rise from the cave floor as a result of the water droplets that have been falling in the same place for millennia, regenerates calcium carbonate.

Water on the ceiling or floor does not evaporate, but calcium carbonate does not, resulting in stactites and stalagmites.