A contribution to the crystal chemistry of ellestadite and the silicate sulfate apatitest
A series of calcium silicate sulfate apatites from Crestmore, California, which contain the coupled substitution Silvsvl for 2Pv, has been investigated using electron microprobe, powder diffraction, and single-crystal diffraction methods. Chemical analysis of eighteen specimens of different phosphorus contents proves that the Si: S ratio is essentially I : I and yields the idealized general formula Caro(SiOn):-*(SO4)3-^@O4)2.(OH,F,CD2, where x : 0 to 3. The members of this series for which x : 0 and 3l2 have been labelled "ellestadite" and "wilkeite", respectively, by previous workers. "Ellestadite" is actually a solid solution involving the end-members Cale(SiO a,){SOq)tZz, where Z: OH (hydroxylellestadite), F (fluorellestadite), or Cl (chlorellestadite). The term ellestadite is redefined to make it a group name for all compositions having >(Si,S) > P. Wilkeite is not a valid mineral species, since it is only one of many solid solutions involving the six end-members fluorapatite, hydroxyapatite, chlorapatite, fluorellestadite, hydroxylellestadite, and chlorellestadite. Although natural hydroxylellestadite is monoclinic, precession photographs of type "ellestadite" and "wilkeite" show hexagonal symmetry and no evidence of Si-S ordering as suggested by the Si: S ratio of I : I . The silicate sulfate apatites from Crestmore show a strong linear relationship between their P and F contents, such that these two variables simultaneously go to zero. Linear relationships also exist between their unit cell parameters and their P, F, and (Si+S) contents. These correlations imply a convergence of the Crestmore apatite series towards a hypothetical memberof composition Caro(SiOa)r (SO4)3(OH,CI)z and cell constants a:9.543 and c = 6.9174.
Phase relations and crystal chemistry of apatite and silicocarnotite solid solutions
Abstract Two phases containing both Si and S occur in cement clinkers. These are solid solutions having the apatite and silicocarnotite structures: the Si and S end-members are ellestadite and calcium silicosulphate, respectively. (F, Cl) ellestadite and phosphate apatites are completely miscible, as are silicocarnotite and silicosulphate. Moreover, ellestadite apatites form extensive halogen-deficient solid solutions with silicosulphate at 800 – 1100°C.
Apatite: Its Crystal Chemistry, Mineralogy, Utilization, and Geologic and Biologic Occurrences
1. Introduction.- 2. Earlier Work on Apatite.- 3. Physical Properties.- 3.1. Density and Dimensions.- 3.2. Optical Properties.- 3.3. Electrical and Other Properties.- 4. Structure.- 5. Crystal Chemistry.- 5.1. Substitutions for Calcium.- 5.2. Substitutions for Phosphorus.- 5.3. Substitutions for Fluorine.- 5.4. Complex Polyionic Substitutions.- 6. Synthetic Apatites: Applications.- 6.1. Phosphors.- 6.2. Synthesis.- 6.3. Phase Relations.- 6.4. Commercial Calcium Phosphate.- 7. Carbonate Apatites.- 7.1. Stoichiometry.- 7.2. Structural Dimensions.- 7.3. Refraction and Absorption.- 7.4. Questionable Interpretations.- 8. Phosphorites.- 8.1. Relations with Sea Water.- 8.2. Geochemistry: Enrichment.- 8.3. Carbonate Content.- 9. Geology: Igneous and Metamorphic Occurrences.- 9.1. Igneous Rocks.- 9.2. Segregations.- 9.3. Veins, Dikes, and Sills.- 9.4. Carbonatites.- 9.5. Metamorphic Rocks.- 9.6. Lunar Rocks and Meteorites.- 10. Biologic Apatites.- 10.1. Teeth and Bones: Composition.- 10.2. Teeth and Bones: Possible Precursors.- 10.3. Teeth and Bones: Mineralization.- 10.4. Teeth and Bones: Trace Elements.- 10.5. Other Biologic Precipitates.- 11. Critique.- References.- Geographical Index and References to Localities.