Order-disorder approach to calcioaravaipaite, [PbCa2Al(F,OH)9]: The crystal structure of the triclinic MDO polytype
-
Anthony R. Kampf
Abstract
The crystal structure of calcioaravaipaite, PbCa2Al(F,OH)9, was initially solved by direct methods in the monoclinic space group A2/m (R = 12.4%). Further study demonstrated the OD nature of the structure, and showed that the crystal was twinned. The structure was solved in the triclinic space group C1̅ , a = 7.722(3), b = 7.516(3), c = 12.206(4) Å, α = 98.86(1), β = 96.91(1), γ = 90.00(1)°, V = 694.8(3) Å3, Z = 4, yielding R = 5.1% for 1420 reflections with Fo > 4σ(Fo).
Calcioaravaipaite belongs to a family of order-disorder (OD) structures formed by equivalent layers of symmetry C2/m. Two maximum-degree-of-order (MDO) polytypes are possible. MDO1 results from a regular alternation of stacking operators 21/2 and 2-1/2 and yields a monoclinic structure with C2/c, a = 7.72, b = 7.52, c = 24.12 Å, β = 96.99°. MDO2 results from the sequence 21/2 / 21/2 / 21/2 /… and yields a triclinic structure with a = 7.72, b = 7.52, c = 12.21 Å, α = 98.86, β = 96.91, γ = 90.00°.
The structure of calcioaravaipaite is comprised of two kinds of alternating polyhedral slabs parallel to (001). Slab 1 consists of a fluorite-like double layer of edge-sharing (CaF8) distorted cubes and slab 2 is a composite of face- and edge-sharing (PbF12) polyhedra and outlying (AlF6) octahedra, the latter sharing faces and edges with the (PbF12) polyhedra, but no elements with one another. Aravaipaite and calcioaravaipaite share a common fluorite-type layer; however, in aravaipaite the presence of Pb2+ rather than Ca2+ in this layer results in slabs of strikingly different polyhedral configuration.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Structure, metal-insulator transitions, and magnetic properties of FeO at high pressures
- The high-temperature behavior of defect hydrogen species in quartz: Implications for hydrogen isotope studies
- Thermal stability and vibrational spectra of the sheet borate tuzlaite, NaCa[B5O8(OH)2]·3H2O
- Hydrogen-bonded water in laumontite I: X-ray powder diffraction study of water site occupancy and structural changes in laumontite during room-temperature isothermal hydration/dehydration
- In-situ determination of mineral solubilities in fluids using a hydrothermal diamond-anvil cell and SR-XRF: Solubility of AgCl in water
- Pressure-induced phase transition in malayaite, CaSnOSiO4
- Equation of state of stishovite to lower mantle pressures
- Chemical transfer during redox exchanges between H2 and Fe-bearing silicate melts
- Trace-element partitioning between alkali feldspar and peralkalic quartz trachyte to rhyolite magma. Part I: Systematics of trace-element partitioning
- Trace-element partitioning between alkali feldspar and peralkalic quartz trachyte to rhyolite magma. Part II: Empirical equations for calculating trace-element partition coefficients of large-ion lithophile, high field-strength, and rare-earth elements
- Four generations of accessory-phase growth in low-pressure migmatites from SW New Hampshire
- Mineralogy, chemistry, and formation of oxidized biotite in the weathering profile of granitic rocks
- Experimental study of zircon coarsening in quartzite ±H2O at 1.0 GPa and 1000 ℃, with implications for geochronological studies of high-grade metamorphism
- Biotite dissolution processes and mechanisms in the laboratory and in nature: Early stage weathering environment and vermiculitization
- Fe2+ -Mg partitioning between garnet, magnesiowüstite, and (Mg,Fe)2SiO4 phases of the transition zone
- Interlayer structure and dynamics of Cl-bearing hydrotalcite: far infrared spectroscopy and molecular dynamics modeling
- Si-Al disorder and solid solutions in analcime, chabazite, and wairakite
- Cafetite, Ca[Ti2O5](H2O): Crystal structure and revision of chemical formula
- Order-disorder approach to calcioaravaipaite, [PbCa2Al(F,OH)9]: The crystal structure of the triclinic MDO polytype
- Ab initio investigation of the structures of NaOH hydrates and their Na+ and OH– coordination polyhedra
- Another step toward understanding the true nature of sartorite: Determination and refinement of a ninefold superstructure
- Letter. Ultrapotassic clinopyroxene from the Kumdy-Kol microdiamond mine, Kokchetav Complex, Kazakhstan: Occurrence, composition and crystal-chemical characterization
- Letter. Determination of planetary basalt parentage: A simple technique using the electron microprobe
Articles in the same Issue
- Structure, metal-insulator transitions, and magnetic properties of FeO at high pressures
- The high-temperature behavior of defect hydrogen species in quartz: Implications for hydrogen isotope studies
- Thermal stability and vibrational spectra of the sheet borate tuzlaite, NaCa[B5O8(OH)2]·3H2O
- Hydrogen-bonded water in laumontite I: X-ray powder diffraction study of water site occupancy and structural changes in laumontite during room-temperature isothermal hydration/dehydration
- In-situ determination of mineral solubilities in fluids using a hydrothermal diamond-anvil cell and SR-XRF: Solubility of AgCl in water
- Pressure-induced phase transition in malayaite, CaSnOSiO4
- Equation of state of stishovite to lower mantle pressures
- Chemical transfer during redox exchanges between H2 and Fe-bearing silicate melts
- Trace-element partitioning between alkali feldspar and peralkalic quartz trachyte to rhyolite magma. Part I: Systematics of trace-element partitioning
- Trace-element partitioning between alkali feldspar and peralkalic quartz trachyte to rhyolite magma. Part II: Empirical equations for calculating trace-element partition coefficients of large-ion lithophile, high field-strength, and rare-earth elements
- Four generations of accessory-phase growth in low-pressure migmatites from SW New Hampshire
- Mineralogy, chemistry, and formation of oxidized biotite in the weathering profile of granitic rocks
- Experimental study of zircon coarsening in quartzite ±H2O at 1.0 GPa and 1000 ℃, with implications for geochronological studies of high-grade metamorphism
- Biotite dissolution processes and mechanisms in the laboratory and in nature: Early stage weathering environment and vermiculitization
- Fe2+ -Mg partitioning between garnet, magnesiowüstite, and (Mg,Fe)2SiO4 phases of the transition zone
- Interlayer structure and dynamics of Cl-bearing hydrotalcite: far infrared spectroscopy and molecular dynamics modeling
- Si-Al disorder and solid solutions in analcime, chabazite, and wairakite
- Cafetite, Ca[Ti2O5](H2O): Crystal structure and revision of chemical formula
- Order-disorder approach to calcioaravaipaite, [PbCa2Al(F,OH)9]: The crystal structure of the triclinic MDO polytype
- Ab initio investigation of the structures of NaOH hydrates and their Na+ and OH– coordination polyhedra
- Another step toward understanding the true nature of sartorite: Determination and refinement of a ninefold superstructure
- Letter. Ultrapotassic clinopyroxene from the Kumdy-Kol microdiamond mine, Kokchetav Complex, Kazakhstan: Occurrence, composition and crystal-chemical characterization
- Letter. Determination of planetary basalt parentage: A simple technique using the electron microprobe
