摘要
The microstructural features of clacium rare earth(Ca RE) fluorocarbonate minerals from Southwest China were studied by using selected area electron diffraction(SAED) and high resolution transmission electron microscopy(HRTEM). Three new regularly mixed layer structures of B 8S 6 type with long period and different stacking sequence, i.e. B 8S 6 Ⅰ, B 8S 6 Ⅱ, and B 8S 6 Ⅲ, were found in the derived polycrystal of parisite, in which their structural symmetry, cell parameters, chemical formulas of crystal and stacking models of structural unit layer, etc. were determined. The results of this study also show that these new regularly mixed layer structrues were formed by order stacking unit layer of bastnaesite(B) and synchisite(S) in varying proportion along c axis. The observation under HRTEM reveals that in the three new regularly mixed layer structures there are different distribution modes of Ce F ion layers, CO 2- 3 ion groups between the Ce F ion layers, and CO 2- 3 ion groups between Ce F and Ca 2+ ion layers, and there are some heterogeneous textures, such as disorder interlayer and stacking fault. It further proves the complexity of the crystal structure of the Ca RE fluorocarbonate minerals.
The microstructural features of clacium rare earth(Ca RE) fluorocarbonate minerals from Southwest China were studied by using selected area electron diffraction(SAED) and high resolution transmission electron microscopy(HRTEM). Three new regularly mixed layer structures of B 8S 6 type with long period and different stacking sequence, i.e. B 8S 6 Ⅰ, B 8S 6 Ⅱ, and B 8S 6 Ⅲ, were found in the derived polycrystal of parisite, in which their structural symmetry, cell parameters, chemical formulas of crystal and stacking models of structural unit layer, etc. were determined. The results of this study also show that these new regularly mixed layer structrues were formed by order stacking unit layer of bastnaesite(B) and synchisite(S) in varying proportion along c axis. The observation under HRTEM reveals that in the three new regularly mixed layer structures there are different distribution modes of Ce F ion layers, CO 2- 3 ion groups between the Ce F ion layers, and CO 2- 3 ion groups between Ce F and Ca 2+ ion layers, and there are some heterogeneous textures, such as disorder interlayer and stacking fault. It further proves the complexity of the crystal structure of the Ca RE fluorocarbonate minerals.
