FTIR Spectroscopy of CO3- and OH-bearing Apatites

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Apatite group minerals are made primarily of calcium and phosphate and contain smaller amounts of chlorine, fluorine, hydroxide, carbonate and sulfate. These minor components can be linked through mathematical models to gases (for example, water and carbon dioxide) that are important in many geological processes that lead not only to formation of ore deposits but also to the causes for explosive volcanism. Apatites are found in a wide variety of rocks. Therefore this study will provide the analytical and intellectual basis for an apatite-based mathematical model for carbon dioxide and water behavior in (solid or molten) rocks from the Earth's mantle to surface. One potential application is determining carbon dioxide contributions from volcanoes into the atmosphere at geologic times associated with climate change. A broader impact of this research lies in its presentation as an integral part of the North Carolina Museum of Natural Sciences' Nature Research Center, an 80,000 square foot facility designed to bring research directly to the general public through a variety of forums and media. Further impact is expected in the understanding of carbonate incorporated into tooth and bone apatite, and in the design of biomaterials. This research addresses fundamental problems with the apatite group minerals, using microanalytical techniques to enhance the thermodynamic data used in mathematical models. The project will include the development of microanalytical methods for apatites such as Fourier Transform Infrared Spectroscopy (FTIR) for the measurement of OH (hydroxyl ion) and CO3 (carbonate group) in combination with Secondary Ion Mass Spectrometry (SIMS). Diffusion of fluorine and chlorine in apatite during Electron Probe Microanalysis (EPMA) will be further examined. Apatites will be synthesized in molten salts at temperatures from 600-800°C, providing a simple system for determining (mathematical) thermodynamic data for the pure end member apatites and for the apatites containing mixtures of fluorine, chlorine and hydroxyl ions, and mixtures of hydroxyl ions and carbonate.