(n.) In caves, limestone is dissolved through the action of acids such as carbonic or sulfuric acids. This is a form of chemical weathering in which a substance such as carbon dioxide or hydrogen sulfide combines with water to form an acid, causing the limestone to dissociate into individual ions such as the calcium (Ca2+) ion and the carbonate ion. Microorganisms also may produce acids as products of their metabolism. These acids may lead to limestone dissolution.