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Crystal structure analyses of four tourmaline specimens from the Cleopatra’s Mines (Egypt) and Jabal Zalm (Saudi Arabia), and the role of Al in the tourmaline group

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Published/Copyright: April 2, 2015
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American Mineralogist
From the journal American Mineralogist Volume 95 Issue 4

Abstract

Fe-rich “oxydravite” and dravite from the Late Proterozoic ophiolitic mélange of the Arabo-Nubian Shield, located in Egypt and Saudi Arabia, were structurally and chemically characterized by using crystal structure refinement based on single-crystal X-ray diffraction data, electron microprobe analysis, and Mössbauer spectroscopy. Structural formulae obtained by optimization procedures indicate disordering of Al, Mg, and Fe2+ over the Y and Z sites, and an ordering of Fe3+ at Y. The disordering can be explained by the substitution mechanisms 2YMg+ZAl+WOH = 2YAl+ZMg+WO2- and 2YFe2++ZFe3++WOH = 2YFe3++ZFe2++WO2-, which are consistent with reducing the mismatch in dimensions between YO6 and ZO6 octahedra.

To explain the Mg-Al disordering process, as well as the occurrence of B at the T site in tourmaline, analogies have been drawn between the crystal structure of tourmaline and that of lizardite. A critical constraint in both structures is the geometrical fit of the six-membered tetrahedral ring with the attached group of three YO6 octahedra. In tourmaline, the disordering of Mg and Al over Y and Z relieves the strain due to the misfit in dimensions of the larger triads of edge-sharing MgO6 octahedra and the smaller Si6O18 tetrahedral rings. In Al-rich tourmaline, where the octahedral cluster is smaller, the strain can be relieved by incorporating B in the tetrahedra. An opposite effect is observed by substitution of Al for Si at the tetrahedral site in Mg-rich tourmaline. Because the Al radius is intermediate between those of Mg and Si, Al plays an important structural role in accommodating the potential misfit between YO6, ZO6, and TO4 polyhedra. The amount of Al and its distribution in the structure strongly affects the values of the unit-cell parameters of tourmaline and yields volume variations according to a quadratic model. This results from the effect of ZAl combined with the occurrence of B at T in Al-rich tourmaline. ZAl has a greater effect than YAl as long as Al does not fully occupy the Z site.

Keywords: Chemical analysis; tourmaline; crystal structure; Mössbauer spectroscopy; orderdisorder; XRD data
Received: 2009-7-27
Accepted: 2009-12-2
Published Online: 2015-4-2
Published in Print: 2010-4-1

© 2015 by Walter de Gruyter Berlin/Boston

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  2. Discovery, mineral paragenesis, and origin of wadalite in a meteorite
  3. Cathodoluminescence microscopy and spectroscopy of synthetic ruby crystals grown by the optical floating zone technique
  4. Structural relaxation around Cr3+ and the red-green color change in the spinel (sensu stricto)-magnesiochromite (MgAl2O4-MgCr2O4) and gahnite-zincochromite (ZnAl2O4-ZnCr2O4) solid-solution series
  5. Recrystallization in fully metamict gadolinite from Ytterby (Sweden), annealed in air and studied by 57Fe Mössbauer spectroscopy
  6. Fantappièite, a new mineral of the cancrinite-sodalite group with a 33-layer stacking sequence: Occurrence and crystal structure
  7. Reinvestigation of the crystal structure of the zeolite gobbinsite: A single-crystal X-ray diffraction study
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  9. Crystal structure and low-temperature behavior of “disordered” thomsonite
  10. Cooling-induced crystallization of microlite crystals in two basaltic pumice clasts
  11. Crystal structure analyses of four tourmaline specimens from the Cleopatra’s Mines (Egypt) and Jabal Zalm (Saudi Arabia), and the role of Al in the tourmaline group
  12. Combined single-crystal X-ray and neutron powder diffraction structure analysis exemplified through full structure determinations of framework and layer beryllate minerals
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  14. Solubility of manganotantalite and manganocolumbite in pegmatitic melts
  15. The effect of silica on ferric/ferrous ratio in silicate melts: An experimental study using Mössbauer spectroscopy
  16. HRTEM investigation of trilling todorokite and nano-phase Mn-oxides in manganese dendrites
  17. Thermo-chemical and thermo-physical properties of the high-pressure phase anhydrous B (Mg14Si5O24): An ab-initio all-electron investigation
  18. The incommensurately modulated structures of natural natrite at 120 and 293 K from synchrotron X-ray data
  19. Sulfide oxidation observed using micro-Raman spectroscopy and micro-X-ray diffraction: The importance of water/rock ratios and pH conditions
  20. In situ measurements of plagioclase growth using SIMS depth profiles of 7Li/30Si: A means to acquire crystallization rates during short-duration decompression events
  21. Crystal chemistry of the MgAl2O4-MgMn2O4-MnMn2O4 system: Analysis of structural distortion in spinel- and hausmannite-type structures
  22. The effect of Al and water on the compressibility of diopside
  23. Geothermometric study of Mg-rich spinels from the Somma-Vesuvius volcanic complex (Naples, Italy)
  24. Serpentine minerals discrimination by thermal analysis
  25. A new type of cubic-stacked layer structure in anthoinite, AlWO3(OH)3
  26. Townendite, Na8ZrSi6O18, a new uranium-bearing lovozerite group mineral from the Ilímaussaq alkaline complex, Southern Greenland
  27. Letter. Pressure-induced transformations in kaolinite
  28. Letter. The crystal structure of gypsum-II determined by single-crystal synchrotron X-ray diffraction data
https://doi.org/10.2138/am.2010.3357
Keywords for this article
Chemical analysis; tourmaline; crystal structure; Mössbauer spectroscopy; orderdisorder; XRD data

Articles in the same Issue

  1. Fe site occupancy in magnetite-ulvöspinel solid solutions: A new approach using X-ray magnetic circular dichroism
  2. Discovery, mineral paragenesis, and origin of wadalite in a meteorite
  3. Cathodoluminescence microscopy and spectroscopy of synthetic ruby crystals grown by the optical floating zone technique
  4. Structural relaxation around Cr3+ and the red-green color change in the spinel (sensu stricto)-magnesiochromite (MgAl2O4-MgCr2O4) and gahnite-zincochromite (ZnAl2O4-ZnCr2O4) solid-solution series
  5. Recrystallization in fully metamict gadolinite from Ytterby (Sweden), annealed in air and studied by 57Fe Mössbauer spectroscopy
  6. Fantappièite, a new mineral of the cancrinite-sodalite group with a 33-layer stacking sequence: Occurrence and crystal structure
  7. Reinvestigation of the crystal structure of the zeolite gobbinsite: A single-crystal X-ray diffraction study
  8. Arsenic-rich fergusonite-beta-(Y) from Mount Cervandone (Western Alps, Italy): Crystal structure and genetic implications
  9. Crystal structure and low-temperature behavior of “disordered” thomsonite
  10. Cooling-induced crystallization of microlite crystals in two basaltic pumice clasts
  11. Crystal structure analyses of four tourmaline specimens from the Cleopatra’s Mines (Egypt) and Jabal Zalm (Saudi Arabia), and the role of Al in the tourmaline group
  12. Combined single-crystal X-ray and neutron powder diffraction structure analysis exemplified through full structure determinations of framework and layer beryllate minerals
  13. Olivine crystal size distributions in kimberlite
  14. Solubility of manganotantalite and manganocolumbite in pegmatitic melts
  15. The effect of silica on ferric/ferrous ratio in silicate melts: An experimental study using Mössbauer spectroscopy
  16. HRTEM investigation of trilling todorokite and nano-phase Mn-oxides in manganese dendrites
  17. Thermo-chemical and thermo-physical properties of the high-pressure phase anhydrous B (Mg14Si5O24): An ab-initio all-electron investigation
  18. The incommensurately modulated structures of natural natrite at 120 and 293 K from synchrotron X-ray data
  19. Sulfide oxidation observed using micro-Raman spectroscopy and micro-X-ray diffraction: The importance of water/rock ratios and pH conditions
  20. In situ measurements of plagioclase growth using SIMS depth profiles of 7Li/30Si: A means to acquire crystallization rates during short-duration decompression events
  21. Crystal chemistry of the MgAl2O4-MgMn2O4-MnMn2O4 system: Analysis of structural distortion in spinel- and hausmannite-type structures
  22. The effect of Al and water on the compressibility of diopside
  23. Geothermometric study of Mg-rich spinels from the Somma-Vesuvius volcanic complex (Naples, Italy)
  24. Serpentine minerals discrimination by thermal analysis
  25. A new type of cubic-stacked layer structure in anthoinite, AlWO3(OH)3
  26. Townendite, Na8ZrSi6O18, a new uranium-bearing lovozerite group mineral from the Ilímaussaq alkaline complex, Southern Greenland
  27. Letter. Pressure-induced transformations in kaolinite
  28. Letter. The crystal structure of gypsum-II determined by single-crystal synchrotron X-ray diffraction data
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