The hydrogen-carbonate ion [(HCO3)] has been detected by Fourier transform infrared (FTIR) spectroscopy in the c-axis structural channel of Na-bearing type A-B carbonate apatite synthesized under conditions of high P (0.1–1 GPa), T (800–1350 °C), and p(CO2), and accounts for up to one-third of the total complement of channel carbonate. The hydrogen-carbonate ion is only loosely bound in the apatite channel, and breaks down on aging at room temperature. Volatile decomposition products are lost from the carbonate apatite structure, with CO2 more mobile than H2O. The mobility of small volatile molecules points to a possible role for the apatite channel in mediating acid-base reactions in restricted surficial environments and biological systems.

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