The Deposition of Calcite and Aragonite in Caves

The conditions controlling the deposition of calcite versus aragonite in caves have been studied. Samples of cave waters and cave deposits have been analyzed. Calcium carbonate has been precipitated in the laboratory under controlled conditions from solutions of calcium bicarbonate containing various added salts. The influence of the composition of the solution on the percentages of calcite and aragonite formed has been studied. Factors directly favoring the formation of aragonite under cave conditions are high temperature, low concentration of calcium bicarbonate, and high concentrations of magnesium, strontium, and lead. The pH, in itself, does not appear to be a controlling factor, though it is related to other important factors. The presence of manganese, barium, or sulfate ions, in concentrations likely to be found in cave waters, does not appear to be effective. Physical factors, including the rate of supply of water to a surface, the area of the surface, and the relative humidity probably operate through their effects on the composition of the solution to influence the formation of calcite versus aragonite.