HR: 0830h
AN: V51D-0317    [PDF]
TI: Structure of Carbonate Apatites Synthesized at 2-4 GPa
AU: * Fleet, M E
EM: mfleet@uwo.ca
AF: University of Western Ontario, Department of Earth Sciences, London, ON N6A5B7 Canada
AU: Liu, X
EM: liux@uwo.ca
AF: University of Western Ontario, Department of Earth Sciences, London, ON N6A5B7 Canada
AU: King, P L
EM: penny.king@uwo.ca
AF: University of Western Ontario, Department of Earth Sciences, London, ON N6A5B7 Canada
AB: Type A carbonate apatite (CAp), type A and B carbonated apatites, and complex type A-B CAp have been synthesized at 2-4 GPa and 1400-1500$\deg C$ in a piston cylinder apparatus, and the accommodation of the carbonate ion studied at NTP using FTIR spectroscopy and X-ray structure analysis. Apatite compositions approximate to Ca$_{10}$(PO$_{4}$)$_{6-y}$(CO$_{3}$)$_{x+(3/2)y}$(OH)$_{2-2x}$, x = 0.0-0.7, y = 0.0-0.6. A new space group (P-3) and structure are reported for type A CAp with x = 0.5-1.0, y = 0.0. The type A carbonate ion is ordered along the apatite channel at z = 0.5; two of its oxygen atoms are close to the c-axis, and the plane of the ion is canted about 12$\deg$. This is the "closed" channel configuration, which is presently labeled "A1". There are three structural locations for the carbonate ion in type A-B CAp (space group P6$_{3}$/m). The channel carbonate is mainly in the closed (A1) configuration (IR bands at 1541 and 1449 cm$^{-1}$), but subordinate amounts are also located in an "open" vertical configuration (A2 carbonate; IR bands at 1563 and 1506 cm$^{-1}$). The type B carbonate ion is located close to the sloping faces of the PO$_{4}$ tetrahedron (IR bands at 1473 and 1406 cm$^{-1}$), and is charge compensated largely by the entry of carbonate into the stuffed A2 channel position. FTIR spectra correspond to CAp synthesized at lower P, and the present structures appear to be appropriate models for accommodation of the carbonate ion in bone and enamel.
DE: 3620 Crystal chemistry
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting