More than 80 mineral species are known to result from secondary chemical reactions in solutional limestone caverns. These minerals are transitional and end-products of carbonate wall rock interactions with ground water and organic residue. Bacteria are often critical in fixing various ions in these reactions. Ultimate source of metallic ions is usually the sulphide minerals weathering in overlying strata, and brought to the cave environment by circulating ground waters. Hydrothermal solutions may bring heavy metallic ion concentrations from deeper strata. About one-third of the known cave mineral species occur in stalactitic form.