Cave Formation
The cave specimens are mainly composed of calcite (CaCO³). Calcite results from the dissolution of limestone, above the caves, due to acidic water dripping from the soil zone. When it reaches the inside of the cave, this water deposits the calcite that it "holds", forming a stalactite or another cavern. It is known that salt is made which crystallizes from the evaporation of water leaving the brine.
Crystallization of Calcite
Since the air in the cave is full of water vapor, the water that enters the cave can not evaporate. What causes dissolved calcite (CaCO³) to crystallize is a completely different process, the loss-escape of carbon dioxide (CO²) gas from water droplets.
The Importance of CO2
In the soil zone, where abundant plant debris decomposes rapidly, the CO² content of soil air can exceed 300 times the proportion of one hundred percent of the outside atmosphere. This CO² combines with the ground water to produce carbonic acid, which flows to dissolve the limestone and through its discontinuities enters the cave. When water comes in contact with cave air, which generally has a partial pressure of CO² much lower than that of ground air, CO² escapes from the water. When CO² escapes, a chemical change occurs, which is expressed by the following reaction: Ca + 2HCO³ → CO² ↑ + CaCO³ + H²O. This process is the opposite of that of limestone dissolution.
The fact that the loss of CO² and, more rarely, the evaporation of water, is the main way in which calcareous cave deposits are formed, is proved by their chemical composition. Stalactites are almost pure calcite, although the water from which they are formed may contain large amounts of other components in solution.
Due to its loss there is only a deposit of calcium carbonate, while the other components are not deposited as would happen in the case of evaporation. the cracks. This happens throughout its flow from the roof of the cave down. But it moves so fast that when it enters the cave it already has calcium carbonate to deposit. It is known from the above that while the deposition can take place outside the caves, the water trapped inside them opens cavities.
