The quantitative determination of limestone in various mixtures is a very important analytical problem for several industrial processes, especially so for the cement and lime industries where the determination of limestone in building-related products is required. Errors can result from the presence of several minerals, such as Ca(OH)(2) and clays, when the common loss-on-ignition method is used. Infrared spectroscopy is one method of quantitatively measuring a specific substance, providing that the vibrational mode used does not overlap with those of other substances present in the mixture. For this reason FT-IR spectroscopy has been used here to illustrate its potential as an analytical tool in the determination of CaCO3 in mixtures of CaCO3 and Ca(OH)(2).