High-pressure study on lead fluorapatite
High-pressure study on lead fluorapatite
American Mineralogist (October 2008) 93 (10): 1581-1584
The compressional behavior of a synthetic lead fluorapatite [Pb (sub 9.35) (PO (sub 4) ) (sub 6) F (sub 2) ] has been investigated in situ up to about 16.7 GPa at 300 K, using a diamond-anvil cell and synchrotron X-ray diffraction. We find that the compressibility of lead fluorapatite is significantly different from that of fluorapatite [Ca (sub 10) (PO (sub 4) ) (sub 6) F (sub 2) ], chlorapatite [Ca (sub 10) (PO (sub 4) ) (sub 6) Cl (sub 2) ], and hydroxylapatite [Ca (sub 10) (PO (sub 4) ) (sub 6) (OH) (sub 2) ]: lead fluorapatite is much more compressible, and elastically isotropic in the investigated pressure range. The pressure-volume data fitted to the third-order Birch-Murnaghan equation yield an isothermal bulk modulus (K (sub T) ) of 54.3(18) GPa and the pressure derivative (K (sub T) ') of 8.1(6). If K (sub T) ' is fixed at 4, the obtained K (sub T) is 68.4(16) GPa, which is approximately only two-thirds of the isothermal bulk modulus of the calcium apatites.