This is Crystal Cave in Sequoia National Park. Cave formations like this one form when limestone is dissolved by acidic water, and then redeposited. How does water become acidic in the first place?
Answer:
As a raindrop falls through the air, it picks up carbon dioxide, becoming a very weak carbonic acid. You drink that same acid anytime you drink a carbonated soda.
Carbonic acid increases the solubility of calcium carbonate, the chemical that limestone is made of. As the rain water flows through cracks in the limestone, a tiny bit is dissolved away. If the water flows into the air of a cave, the change in temperature and pressure causes it to give up some of its carbon dioxide. That reduces the amount of calcium carbonate that the water can dissolve, so some of it is deposited, forming stalactites, stalagmites, flowstone, etc.
Carbonic acid increases the solubility of calcium carbonate, the chemical that limestone is made of. As the rain water flows through cracks in the limestone, a tiny bit is dissolved away. If the water flows into the air of a cave, the change in temperature and pressure causes it to give up some of its carbon dioxide. That reduces the amount of calcium carbonate that the water can dissolve, so some of it is deposited, forming stalactites, stalagmites, flowstone, etc.
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