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Cave formations are called speleothem, from the Greek word spelaion, cave and thema meaning deposit. Almost all of them are made of calcite, the crystal of calcium carbonate. Different minerals and different movements in the water account for an incredible variety of cave formations.
It was this sulfuric acid that dissolved the limestone forming the caves. Either way, because the soluble limestone is partially dissolved and carried away, these are a type of solutional cave. Less common solutional caves are formed in other types of rock like chalk, marble or gypsum. Often limestone caves are named caverns.