Evolution of Apatites in the Diagenesis

Apatites occurring in sedimentary rocks are carbonate fluorapatites （C-F apatites） with differentCO;contents. During diagenesis. the CO;in the C-F apatites gradually decreased with the increasing strengthof diagenesis. resulting in the systematic changes in refractive index. specific gravity, cell parameters and crystalchemistry of apatites. On the basis of X-ray diffraction and IR spectroscopic analyses, the author proposes twoparameters for determining diagenetic stages. i.e.. the crystallinity index （CR） and sharpness index （SH）. Thesetwo parameters serve as new criteria for the determination. which due to the common existence of phosphorousnodules and bands and argillo-crystalline cement in sedimentary rocks, most likely have wide prospects for ap-plication.