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VIII(Mg,Fe)0.85VI(Mg,Fe)4IV(Fe,Ge)3O12: A new tetragonal phase and its comparison with garnet

  • David Lévy Barbier and Jacques Barbier EMAIL logo
Published/Copyright: March 26, 2015
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American Mineralogist
From the journal American Mineralogist Volume 85 Issue 7-8

Abstract

Tetragonal Mg2.12Fe3.17Ge2.56O12 is a new germanate forming at 1 atm pressure in the MgO-Fe2O3- GeO2 system. It is an analogue of the high-pressure silicate mineral TAPP occurring as inclusions in diamonds of lower-mantle origin. Its crystal structure was determined by X-ray diffraction using single-crystals grown from a potassium molybdate flux. It crystallizes in the I4̄2d space group with a = 6.8153(4) Å, c = 18.669(2) Å, Z = 4. The refinement of its cation distribution, VIII(Mg0.52Fe0.33)VI(Mg1.60Fe2.40)IV(Ge2.56Fe0.44)O12, shows the presence of a partially filled (85%) dodecahedral site characterized by an unusual geometry with two very different bond lengths [2.169 Å (×4) and 2.609 Å (×4)]. The structure determinations of the Ca2+- and Y3+-substituted phases show that the larger cations are completely partitioned in the dodecahedral site, increasing its occupancy slightly (up to 92% in the case of Ca2+). Cubic Mg2.35Y2.00Fe0.97Ge2.59O12 is a new garnet phase forming at 1 atm pressure in the MgO-Y2O3-Fe2O3-GeO2 system. Its crystal structure and cation distribution were also determined by singlecrystal X-ray diffraction: VIII(MgY2)VI(Mg1.35Fe0.56)IV(Ge2.59Fe0.41)O12, Ia3̄d space group, a = 12.232(1) Å, Z = 8. In spite of similarities in their chemical compositions, the tetragonal and garnet phases are structurally distinct, with different ratios of dodecahedral to octahedral sites, viz., VIIIAVIB4IVT3O12 and VIIIA3VIB2IVT3O12 respectively. As a consequence, the tetragonal phase forms in systems containing smaller cations, such as Mg2+, Fe3+, Ni2+, Co2+, whereas larger cations, such as Y3+, show a strong preference for the garnet phase.

Received: 1999-9-7
Accepted: 2000-2-29
Published Online: 2015-3-26
Published in Print: 2000-7-1

© 2015 by Walter de Gruyter Berlin/Boston

Articles in the same Issue

  1. Application of new experimental and garnet Margules data to the garnet-biotite geothermometer
  2. Volumes of mixing in aluminosilicate garnets: Solid solution and strain behavior
  3. Cerium anomaly and Th/U fractionation in the 1.85 Ga Flin Flon Paleosol: Clues from REE- and U-rich accessory minerals and implications for paleoatmospheric reconstruction
  4. Os solubility in silicate melts: New efforts and results
  5. Enstatite-forsterite-water equilibria at elevated temperatures and pressures
  6. The OH-F substitution in synthetic pargasite at 1.5 kbar, 850 °C
  7. Uptake of aqueous Pb by Cl-, F–, and OH– apatites: Mineralogic evidence for nucleation mechanisms
  8. Temperature dependence of the hyperfine parameters of synthetic P21/c Mg-Fe clinopyroxenes along the MgSiO3-FeSiO3 join
  9. Single-crystal thermometric calibration of Fe-Mg order-disorder in pigeonites
  10. TEM observations on the P1̄ -I1̄ phase transition in feldspars along the join CaAl2Si2O8-SrAl2Si2O8
  11. Phase transitions induced by solid solution in stuffed derivatives of quartz: A powder synchrotron XRD study of the LiAlSiO4-SiO2 join
  12. The transformation of andalusite to mullite and silica: Part I. Transformation mechanism in [001]A direction
  13. The transformation of andalusite to mullite and silica: Part II. Transformation mechanisms in [100]A and [010]A directions
  14. Structure and twinning of tetragonal Ca3Mn2Ge3O12 garnet
  15. The equation of state of lawsonite to 7 GPa and 873 K, and calculation of its high pressure stability
  16. Boron K-edge XANES of borate and borosilicate minerals
  17. 113Cd double-resonance NMR as a probe of clay mineral cation exchange sites
  18. Solid state NMR study of oxygen site exchange and Al-O-Al site concentration in analcime
  19. Isomorphous substitution effect on the vibration frequencies of hydroxyl groups in molecular cluster models of the clay octahedral sheet
  20. Molecular modeling of the structure and dynamics of the interlayer and surface species of mixed-metal layered hydroxides: Chloride and water in hydrocalumite (Friedel’s salt)
  21. VIII(Mg,Fe)0.85VI(Mg,Fe)4IV(Fe,Ge)3O12: A new tetragonal phase and its comparison with garnet
  22. Rietveld analysis of dicalcium aluminate (Ca2Al2O5) – A new high pressure phase with the Brownmillerite-type structure
  23. Suredaite, PbSnS3, a new mineral species, from the Pirquitas Ag-Sn deposit, NW-Argentina: mineralogy and crystal structure
  24. Kozoite-(Nd), Nd(CO3)(OH), a new mineral in an alkali olivine basalt from Hizen-cho, Saga Prefecture, Japan
  25. Florenskyite, FeTiP, a new phosphide from the Kaidun meteorite
  26. Letters. Computer simulation of high-temperature, forsterite-melt partitioning
https://doi.org/10.2138/am-2000-0721

Articles in the same Issue

  1. Application of new experimental and garnet Margules data to the garnet-biotite geothermometer
  2. Volumes of mixing in aluminosilicate garnets: Solid solution and strain behavior
  3. Cerium anomaly and Th/U fractionation in the 1.85 Ga Flin Flon Paleosol: Clues from REE- and U-rich accessory minerals and implications for paleoatmospheric reconstruction
  4. Os solubility in silicate melts: New efforts and results
  5. Enstatite-forsterite-water equilibria at elevated temperatures and pressures
  6. The OH-F substitution in synthetic pargasite at 1.5 kbar, 850 °C
  7. Uptake of aqueous Pb by Cl-, F–, and OH– apatites: Mineralogic evidence for nucleation mechanisms
  8. Temperature dependence of the hyperfine parameters of synthetic P21/c Mg-Fe clinopyroxenes along the MgSiO3-FeSiO3 join
  9. Single-crystal thermometric calibration of Fe-Mg order-disorder in pigeonites
  10. TEM observations on the P1̄ -I1̄ phase transition in feldspars along the join CaAl2Si2O8-SrAl2Si2O8
  11. Phase transitions induced by solid solution in stuffed derivatives of quartz: A powder synchrotron XRD study of the LiAlSiO4-SiO2 join
  12. The transformation of andalusite to mullite and silica: Part I. Transformation mechanism in [001]A direction
  13. The transformation of andalusite to mullite and silica: Part II. Transformation mechanisms in [100]A and [010]A directions
  14. Structure and twinning of tetragonal Ca3Mn2Ge3O12 garnet
  15. The equation of state of lawsonite to 7 GPa and 873 K, and calculation of its high pressure stability
  16. Boron K-edge XANES of borate and borosilicate minerals
  17. 113Cd double-resonance NMR as a probe of clay mineral cation exchange sites
  18. Solid state NMR study of oxygen site exchange and Al-O-Al site concentration in analcime
  19. Isomorphous substitution effect on the vibration frequencies of hydroxyl groups in molecular cluster models of the clay octahedral sheet
  20. Molecular modeling of the structure and dynamics of the interlayer and surface species of mixed-metal layered hydroxides: Chloride and water in hydrocalumite (Friedel’s salt)
  21. VIII(Mg,Fe)0.85VI(Mg,Fe)4IV(Fe,Ge)3O12: A new tetragonal phase and its comparison with garnet
  22. Rietveld analysis of dicalcium aluminate (Ca2Al2O5) – A new high pressure phase with the Brownmillerite-type structure
  23. Suredaite, PbSnS3, a new mineral species, from the Pirquitas Ag-Sn deposit, NW-Argentina: mineralogy and crystal structure
  24. Kozoite-(Nd), Nd(CO3)(OH), a new mineral in an alkali olivine basalt from Hizen-cho, Saga Prefecture, Japan
  25. Florenskyite, FeTiP, a new phosphide from the Kaidun meteorite
  26. Letters. Computer simulation of high-temperature, forsterite-melt partitioning
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