Evolution of Apatites in the Diagenesis

Apatites occurring in sedimentary rocks are carbonate fluorapatites (C-F apatites) with differentCO_2 contents. During diagenesis. the CO_2 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.

Evolution of Apatites in the Diagenesis

Abstract Apatites occurring in sedimentary rocks are carbonate fluorapatites (C-F apatites) with different CO₂ contents. During diagenesis, the C₂ in the C-F apatites gradually decreased with the increasing strength of diagenesis, resulting in the systematic changes in refractive index, specific gravity, cell parameters and crystal chemistry of apatites. On the basis of X-ray diffraction and IR spectroscopic analyses, the author proposes two parameters for determining diagenetic stages, i.e., the crystallinity index (CR) and sharpness index (SH). These two parameters serve as new criteria for the determination, which due to the common existence of phosphorous nodules and bands and argillo-crystalline cement in sedimentary rocks, most likely have wide prospects for application.