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Oxy-dravite, Na(Al2Mg)(Al5Mg)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup

  • Ferdinando Bosi EMAIL logo and Henrik Skogby
Published/Copyright: March 7, 2015
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American Mineralogist
From the journal American Mineralogist Volume 98 Issue 8-9

Abstract

Oxy-dravite, Na(Al2Mg)(Al5Mg)(Si6O18)(BO3)3(OH)3O, is a new mineral of the tourmaline supergroup. The holotype specimen originates from the locality of Osarara (Narok district, Kenya) and occurs in quartz-muscovite schist. Crystals of oxy-dravite are dark red, partially translucent with a vitreous luster, a pink streak, and conchoidal fracture. It has a Mohs hardness of approximately 7, and a calculated density of 3.073 g/cm3. In plane-polarized light, oxy-dravite is pleochroic (O = orange and E = pink) and uniaxial negative: ω = 1.650(5), ε = 1.620(5). Oxy-dravite is rhombohedral, space group R3m, with the unit-cell parameters a = 15.9273(2) and c = 7.2001(1) Å, V = 1581.81(4) Å3, Z = 3. Chemical characterization based on electron microprobe analysis, single-crystal structure refinement, Mössbauer, and optical spectroscopy, resulted in the empirical structural formula:

X(Na0.83□0.15K0.02)∑1.00Y(Al1.34Fe3+0.58Mg1.03Fe2+0.03Ti0.02)∑3.00Z(Al4.95Mg1.03Fe3+0.02)∑6.00T(Si5.98Al0.02O18)∑6.00B(BO3)3V(OH)3W(O0.76OH0.24)∑1.00.

While the end-member formula of oxy-dravite may be formalized as NaY(Al3)Z(Al4Mg2) Si6O18(BO3)3(OH)3O, the most representative structural formula is NaY(Al2Mg)Z(Al5Mg) Si6O18(BO3)3(OH)3O. The difference between these two formulas is solely in Al-Mg order-disorder, i.e., there is no difference in chemical composition. Although the Mg-Al disorder over the Y and Z sites is controlled by the short-range bond-valence requirements of O2- at the O1 (≡W) site, the amount of Mg at the Z site is a function of the degree of cation size mismatch at Z.

The crystal structure of oxy-dravite was refined to statistical index R1 of 1.17% using 1586 equivalent reflections collected with MoKα X-radiation. Oxy-dravite is chemically related to dravite (and fluor-dravite), NaMg3Al6Si6O18(BO3)3(OH)3(OH,F), by the heterovalent substitution Al3+ + O2- → Mg2+ + (OH,F)1-.

Keywords : Oxy-dravite; tourmaline; new mineral species; crystal-structure refinement; electron microprobe; Mössbauer spectroscopy; order-disorder
Received: 2012-12-19
Accepted: 2013-4-24
Published Online: 2015-3-7
Published in Print: 2013-8-1

© 2015 by Walter de Gruyter Berlin/Boston

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  1. Editorial. Why you should publish your best papers in American Mineralogist: An International Journal of Earth and Planetary Materials
  2. Highlights and Breakthroughs. New constraints on the size of chondrite parent bodies
  3. Actinides in Geology, Energy, and the Environment. Further investigation of the initial fission-track length and geometry factor in apatite fission-track thermochronology
  4. Versatile monazite: Resolving geological records and solving challenges in materials science. Carboniferous inherited grain and age zoning of monazite and xenotime from leucogranites in far-eastern Nepal: Constraints from electron probe microanalysis
  5. Versatile monazite: Resolving geological records and solving challenges in materials science. Diffusion of helium in natural monazite, and preliminary results on He diffusion in synthetic light rare earth phosphates
  6. Crystal structure of the high-pressure phase of calcium hydroxide, portlandite: In situ powder and single-crystal X-ray diffraction study
  7. Experimental development of patch perthite from synthetic cryptoperthite: Microstructural evolution and chemical re-equilibration
  8. Oxy-dravite, Na(Al2Mg)(Al5Mg)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup
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  15. Influence of temperature and Cl on the hydrothermal replacement of calcite by apatite and the development of porous microstructures
  16. Ordering state in orthopyroxene as determined by precession electron diffraction
  17. Interlayer water molecules in organocation-exchanged vermiculite and montmorillonite: A case study of tetramethylammonium
  18. Spectroscopic and X-ray diffraction investigation of the behavior of hanksite and tychite at high pressures, and a model for the compressibility of sulfate minerals
  19. Low-temperature magnetism of alabandite: Crucial role of surface oxidation
  20. Crystallographic and spectroscopic characterization of Fe-bearing chromo-aluminopovondraite and its relations with oxy-chromium-dravite and oxy-dravite
  21. Experimental determination of siderite stability at high pressure
  22. Relationships among channel topology and atomic displacements in the structures of Pb5(BO4)3Cl with B = P (pyromorphite), V (vanadinite), and As (mimetite)
  23. The crystal structure of johnbaumite, Ca5(AsO4)3OH, the arsenate analogue of hydroxylapatite
  24. A comparison of the Ca3(PO4)2 and CaSiO3 systems, with a new structure refinement of tuite synthesized at 15 GPa and 1300 °C
  25. The system K2CO3-MgCO3 at 6 GPa and 900–1450 °C
  26. Influence of H2 fluid on the stability and dissolution of Mg2SiO4 forsterite under high pressure and high temperature
  27. Crystal chemistry of Cu-bearing tourmalines
  28. Lead-tellurium oxysalts from Otto Mountain near Baker, California: XI. Eckhardite, (Ca,Pb)Cu2+Te6+O5(H2O), a new mineral with HCP stair-step layers
  29. Neutron diffraction in gemology: Single-crystal diffraction study of brazilianite, NaAl3(PO4)2(OH)4
https://doi.org/10.2138/am.2013.4441
Keywords for this article
Oxy-dravite; tourmaline; new mineral species; crystal-structure refinement; electron microprobe; Mössbauer spectroscopy; order-disorder

Articles in the same Issue

  1. Editorial. Why you should publish your best papers in American Mineralogist: An International Journal of Earth and Planetary Materials
  2. Highlights and Breakthroughs. New constraints on the size of chondrite parent bodies
  3. Actinides in Geology, Energy, and the Environment. Further investigation of the initial fission-track length and geometry factor in apatite fission-track thermochronology
  4. Versatile monazite: Resolving geological records and solving challenges in materials science. Carboniferous inherited grain and age zoning of monazite and xenotime from leucogranites in far-eastern Nepal: Constraints from electron probe microanalysis
  5. Versatile monazite: Resolving geological records and solving challenges in materials science. Diffusion of helium in natural monazite, and preliminary results on He diffusion in synthetic light rare earth phosphates
  6. Crystal structure of the high-pressure phase of calcium hydroxide, portlandite: In situ powder and single-crystal X-ray diffraction study
  7. Experimental development of patch perthite from synthetic cryptoperthite: Microstructural evolution and chemical re-equilibration
  8. Oxy-dravite, Na(Al2Mg)(Al5Mg)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup
  9. Behavior of gold in a magma at sulfide-sulfate transition: Revisited
  10. A disordered nanoparticle model for 6-line ferrihydrite
  11. NanoSIMS Pb/Pb dating of tranquillityite in high-Ti lunar basalts: Implications for the chronology of high-Ti volcanism on the Moon
  12. Iron sulfide stoichiometry as a monitor of sulfur fugacity in gas-mixing experiments
  13. Relaxation effects and re-entrant spin glass behavior at low temperatures in natural strunzite, ferristrunzite, and ferrostrunzite
  14. Enthalpies of formation of Fe-Ni monosulfide solid solutions
  15. Influence of temperature and Cl on the hydrothermal replacement of calcite by apatite and the development of porous microstructures
  16. Ordering state in orthopyroxene as determined by precession electron diffraction
  17. Interlayer water molecules in organocation-exchanged vermiculite and montmorillonite: A case study of tetramethylammonium
  18. Spectroscopic and X-ray diffraction investigation of the behavior of hanksite and tychite at high pressures, and a model for the compressibility of sulfate minerals
  19. Low-temperature magnetism of alabandite: Crucial role of surface oxidation
  20. Crystallographic and spectroscopic characterization of Fe-bearing chromo-aluminopovondraite and its relations with oxy-chromium-dravite and oxy-dravite
  21. Experimental determination of siderite stability at high pressure
  22. Relationships among channel topology and atomic displacements in the structures of Pb5(BO4)3Cl with B = P (pyromorphite), V (vanadinite), and As (mimetite)
  23. The crystal structure of johnbaumite, Ca5(AsO4)3OH, the arsenate analogue of hydroxylapatite
  24. A comparison of the Ca3(PO4)2 and CaSiO3 systems, with a new structure refinement of tuite synthesized at 15 GPa and 1300 °C
  25. The system K2CO3-MgCO3 at 6 GPa and 900–1450 °C
  26. Influence of H2 fluid on the stability and dissolution of Mg2SiO4 forsterite under high pressure and high temperature
  27. Crystal chemistry of Cu-bearing tourmalines
  28. Lead-tellurium oxysalts from Otto Mountain near Baker, California: XI. Eckhardite, (Ca,Pb)Cu2+Te6+O5(H2O), a new mineral with HCP stair-step layers
  29. Neutron diffraction in gemology: Single-crystal diffraction study of brazilianite, NaAl3(PO4)2(OH)4
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