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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

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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

Optical absorption spectra of flux-grown single crystals in the spinel s.s.-magnesiochromite and gahnite-zincochromite solid solutions were recorded with the aim of exploring variations in local Cr-O bond distance as a function of composition. With increasing Cr contents, the crystals vary in color from pale red to intensely red to dark greenish. These variations are reflected in the optical spectra by the position and intensity of the two spin-allowed electronic d-d transitions in six-coordinated Cr3+ at ~18 000 (ν1) and 25 000 cm-1 (ν2). From the shift of the ν1 band position, a decrease in crystal field splitting, 10Dq, for six-coordinated Cr3+ with increasing Cr contents is evident in both solid-solution series. Based on published Cr-O bond distances for the CrO6 polyhedra in magnesiochromite and zincochromite of 1.995 and 1.991 Å, respectively, and applying the ligand field relationships, local Cr-O bond distances in gahnite and spinel with Cr contents at trace levels are determined to be 1.974(2) and 1.960(3) Å, respectively. These local Cr-O distances result in relaxation parameters (ε) equal to 0.69(2) and 0.60(3) for Cr-O bonds in the Mg(Al1-xCrx)2O4 and Zn(Al1-xCrx)2O4 series, respectively. However, the presently obtained Racah B values indicate increasing Cr-O bond covalency with increasing Cr3+ contents. This suggests that color changes and accompanying 10Dq variations may be due to variations in Cr-O bond covalency along the two solid-solution series, without or with very minor local Cr-O bond distance variation. Consequently, the ε values obtained from the present optical absorption spectra should be regarded as minimum values.

Keywords: Crystal synthesis; optical spectroscopy; structural relaxation; spinel; gahnite; Cr3+
Received: 2009-8-31
Accepted: 2009-10-27
Published Online: 2015-4-2
Published in Print: 2010-4-1

© 2015 by Walter de Gruyter Berlin/Boston

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  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
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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
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  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
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  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
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https://doi.org/10.2138/am.2010.3388
Keywords for this article
Crystal synthesis; optical spectroscopy; structural relaxation; spinel; gahnite; Cr3+

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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