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Structure and twinning of tetragonal Ca3Mn2Ge3O12 garnet

  • Stefan Heinemann EMAIL logo and Ronald Miletich
Published/Copyright: March 26, 2015
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American Mineralogist
From the journal American Mineralogist Volume 85 Issue 7-8

Abstract

Single crystals of tetragonal Ca3Mn2Ge3O12 garnet (space group symmetry I41/a, a = 12.3098(7) Å, c = 12.3277(9) Å) were characterized by X-ray diffraction and transmission electron microscopy. Their structure is topologically isosymmetric to tetragonal high-pressure garnets such as majorite, displaying the same two distinct types of macroscopic twin mechanisms. Twinning occurs as pseudomerohedral ferroelastic twin lamellae with preferred orientation of the twin-domain boundaries parallel to {101}tet, whereas merohedral ferrobielastic twin domains occur without any orientational preference. The crystal structure was determined from single-crystal X-ray diffraction data of a crystal fragment completely free of pseudo-merohedral twin domains. It shows two different Jahn- Teller distorted MnO6 octahedra, with a different orientation of the axis of polyhedral elongation. The ordering scheme of these Jahn-Teller distorted octahedra follows in an alternating pattern the densest rod packing, and the cooperative effect of the electronically induced octahedral distortion was found to be responsible for the cubic-to-tetragonal symmetry breaking in Ca3Mn2Ge3O12 garnet. The extent of polyhedral distortion indicates a partially dynamic character of the Jahn-Teller effect. The distortion of the tetrahedral T2 sites controls the cooperative effect of the lattice strain induced by the Jahn-Teller distortion of the Mn3+ octahedra and thus is responsible for the overall lower symmetry.

Received: 1999-5-17
Accepted: 2000-2-10
Published Online: 2015-3-26
Published in Print: 2000-7-1

© 2015 by Walter de Gruyter Berlin/Boston

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  13. The transformation of andalusite to mullite and silica: Part II. Transformation mechanisms in [100]A and [010]A directions
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https://doi.org/10.2138/am-2000-0714

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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