Site preference of U and Th in Cl, F, and Sr apatites
-
Yun Luo
,
John M. Hughes
Abstract
Crystals of U- and Th-doped fluor-, chlor-, and strontium-apatite have been synthesized from phosphate-halide-rich melts, and their structures were refined at room temperature with single-crystal X-ray diffraction intensities to R = 0.0167-0.0255. Structure refinements of U-doped fluorapatites indicate that U substitutes almost exclusively into the Ca2 site with site occupancy ratios UCa2/UCa1 that range from 5.00 to 9.33. Similarly, structure refinements of Th-doped fluorapatites indicate that Th substitutes dominantly into the Ca2 site with ThCa2/ThCa1 values that range from 4.33 to 8.67. Structure refinements of U-doped chlorapatites show that U is essentially equally distributed between the two Ca sites with UCa2/UCa1 values that range from 0.89 to 1.17. Results for Th-doped chlorapatites show that Th substitutes into both Ca1 and Ca2 sites with ThCa2/ThCa1 values that range from 0.61 to 0.67. In the Th-doped strontium-apatites with F and Cl end-members, Th is incorporated into both the Ca1 and Ca2 sites. The range of ThCa2/ThCa1 values is 0.56 to 1.00 for the F end-member, and 0.39 to 0.94 for the Cl end-member. XANES measurements of the U-doped samples indicate that U in fluorapatite is tetravalent, whereas in chlorapatite it is heterovalent but dominantly hexavalent.
According to our calculation, the volume of the Ca2 polyhedron increases by about 5.8% from fluorapatite to chlorapatite, but that of Ca1 polyhedron increases by only 0.59%. We speculate that the much greater size of the Ca2 polyhedron in chlorapatite may diminish the selectivity of this position for U and Th. The incorporation of U and Th into fluorapatite results in a decrease in the size of both Ca polyhedra, but the incorporation of U and Th into chlorapatite results in an increase in the volume of both Ca polyhedra. We suggest that the preference of U and Th for both Ca sites in chlorapatite is attributable to the large increase in size and distortion of the Ca2 polyhedron upon substitution of Cl for F.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Determination of high-pressure phase equilibria of Fe2O3 using the Kawai-type apparatus equipped with sintered diamond anvils
- Suhailite, a new ammonium trioctahedral mica
- First record of K-cymrite in North Qaidam UHP eclogite, Western China
- Stability of uranium (VI) peroxide hydrates under ionizing radiation
- Heat capacities and thermodynamic functions of TiO2 anatase and rutile: Analysis of phase stability
- The behavior of Co and Ni in olivine in planetary basalts: An experimental investigation
- Partitioning of Ni between olivine and an iron-rich basalt: Experiments, partition models, and planetary implications
- The application of Lorentz transmission electron microscopy to the study of lamellar magnetism in hematite-ilmenite
- A Monte Carlo study of short- and long-range order of tetrahedral cations in sapphirine and khmaralite
- High-pressure ammonium-bearing silicates: Implications for nitrogen and hydrogen storage in the Earth’s mantle
- Formation of aragonite mesocrystals and implication for biomineralization
- U-Pb age, trace-element, and Hf-isotope compositions of zircon in a quartz vein from eclogite in the western Dabie Mountains: Constraints on fluid flow during early exhumation of ultrahigh-pressure rocks
- Interaction of phosphate-bearing solutions with gypsum: Epitaxy and induced twinning of brushite (CaHPO4·2H2O) on the gypsum cleavage surface
- Fukalite: An example of an OD structure with two-dimensional disorder
- Chemical control of 3T stacking order in a Li-poor biotite mica
- Site preference of U and Th in Cl, F, and Sr apatites
- High-pressure structural behavior of ingersonite, Ca3Mn2+Sb5+4O14: An in-situ single-crystal X-ray study
- Crystal chemistry of Fe32+Cr2Si3O12–Fe32+Fe23+Si3O12 garnet solid solutions and related spinels
- A method to synthesize large fluid inclusions in quartz at controlled times and under unfavorable growth conditions
- The stability of methane hydrate intercalates of montmorillonite and nontronite: Implications for carbon storage in ocean-floor environments
- Structure and carbonate orientation of vaterite (CaCO3)
- Qusongite (WC): A new mineral
- Nanoscale “liquid” inclusions of As-Fe-S in arsenian pyrite
- Water speciation in hydrous silicate and aluminosilicate glasses: Direct evidence from 29Si-1H and 27Al-1H double-resonance NMR
- Acid production by FeSO4·nH2O dissolution and implications for terrestrial and martian aquatic systems
Articles in the same Issue
- Determination of high-pressure phase equilibria of Fe2O3 using the Kawai-type apparatus equipped with sintered diamond anvils
- Suhailite, a new ammonium trioctahedral mica
- First record of K-cymrite in North Qaidam UHP eclogite, Western China
- Stability of uranium (VI) peroxide hydrates under ionizing radiation
- Heat capacities and thermodynamic functions of TiO2 anatase and rutile: Analysis of phase stability
- The behavior of Co and Ni in olivine in planetary basalts: An experimental investigation
- Partitioning of Ni between olivine and an iron-rich basalt: Experiments, partition models, and planetary implications
- The application of Lorentz transmission electron microscopy to the study of lamellar magnetism in hematite-ilmenite
- A Monte Carlo study of short- and long-range order of tetrahedral cations in sapphirine and khmaralite
- High-pressure ammonium-bearing silicates: Implications for nitrogen and hydrogen storage in the Earth’s mantle
- Formation of aragonite mesocrystals and implication for biomineralization
- U-Pb age, trace-element, and Hf-isotope compositions of zircon in a quartz vein from eclogite in the western Dabie Mountains: Constraints on fluid flow during early exhumation of ultrahigh-pressure rocks
- Interaction of phosphate-bearing solutions with gypsum: Epitaxy and induced twinning of brushite (CaHPO4·2H2O) on the gypsum cleavage surface
- Fukalite: An example of an OD structure with two-dimensional disorder
- Chemical control of 3T stacking order in a Li-poor biotite mica
- Site preference of U and Th in Cl, F, and Sr apatites
- High-pressure structural behavior of ingersonite, Ca3Mn2+Sb5+4O14: An in-situ single-crystal X-ray study
- Crystal chemistry of Fe32+Cr2Si3O12–Fe32+Fe23+Si3O12 garnet solid solutions and related spinels
- A method to synthesize large fluid inclusions in quartz at controlled times and under unfavorable growth conditions
- The stability of methane hydrate intercalates of montmorillonite and nontronite: Implications for carbon storage in ocean-floor environments
- Structure and carbonate orientation of vaterite (CaCO3)
- Qusongite (WC): A new mineral
- Nanoscale “liquid” inclusions of As-Fe-S in arsenian pyrite
- Water speciation in hydrous silicate and aluminosilicate glasses: Direct evidence from 29Si-1H and 27Al-1H double-resonance NMR
- Acid production by FeSO4·nH2O dissolution and implications for terrestrial and martian aquatic systems
