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Crystal chemistry of synthetic Ti-Mg-bearing hibonites: A single-crystal X-ray study

  • Mattia Giannini EMAIL logo , Tiziana Boffa Ballaran and Falko Langenhorst
Published/Copyright: October 14, 2014
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American Mineralogist
From the journal American Mineralogist Volume 99 Issue 10

Abstract

Hibonite single crystals were synthesized using two different techniques: hot-pressing of polycrystalline hibonite by means of piston-cylinder apparatus and solid state reaction using citrate-based sol-gel precursors. Chemical analyses, UV/Vis spectroscopy, and single-crystal X-ray characterization were performed on four sets of Ti-Mg-bearing hibonites to investigate the substitution mechanism of Ti3+, Ti4+, and Mg2+, relevant for hibonites found in calcium-aluminum-rich inclusions in meteorites. The unit-cell volume of hibonite depends linearly on the concentration of Ti and Mg: V = 8.21(3)·(Titot + Mg)apfu + 586.06(1). Structural refinements, carried out in the space group P63/mmc, demonstrate that Ti occupies two sites: M2, a trigonal bipyramid, and M4, a distorted octahedron occurring in facesharing pairs. The Ti occupancy factor was refined at both sites. Due to the repulsion of neighboring Ti cations the bond distance M4-O3 increases with increasing Ti content and the cations are displaced from the central position of the polyhedron. The displacement factors (U33)M2 and the site occupancy factor for Ti in the M2 site positively correlate for the samples, which have more than 0.3-0.4 Tiapfu, while (U33)M2 remains that of pure hibonite for small Ti occupancies at the M2 site. This plateau of displacement factor reflects the local strain fields around the substituted Ti atoms and its magnitude indicates that these strain fields begin to overlap at a Ti-Ti separation of about 1-2 unit cells. For a sample synthesized at low oxygen fugacity we detected Ti3+ by means of UV/Vis absorption spectroscopy. The presence of Ti3+ has a clear effect on the M4-M4 distance, which deviates from the linear trend described by samples containing mainly Ti4+. The average bond length M3-O depends linearly on the Mg content of these synthetic hibonites clearly indicating that Mg occupies this site.

Keywords: Hibonite; X-ray diffraction; single crystal; calcium hexaluminates; titanium
Received: 2013-5-7
Accepted: 2014-4-17
Published Online: 2014-10-14
Published in Print: 2014-10-1

© 2014 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am-2014-4592
Keywords for this article
Hibonite; X-ray diffraction; single crystal; calcium hexaluminates; titanium

Articles in the same Issue

  1. Highlights and Breakthroughs. Pauling’s rules, in a world of non-spherical atoms
  2. Highlights and Breakthroughs. Theoretical and applied implications of the structural order of irradiated vermiculite
  3. Highlights and Breakthroughs. An examination of the Ti-in-quartz thermobarometer in rocks that contain dynamically recrystallized quartz: Re-equilibration of [Ti] during recrystallization
  4. The Second Conference on the Lunar Highlands Crust and New Directions. Visible-infrared spectral properties of iron-bearing aluminate spinel under lunar-like redox conditions
  5. The Second Conference on the Lunar Highlands Crust and New Directions. VNIR spectral variability of the igneous stratified Stillwater Complex: A tool to map lunar highlands
  6. The Second Conference on the Lunar Highlands Crust and New Directions. Spinel-rich lithologies in the lunar highland crust: Linking lunar samples with crystallization experiments and remote sensing
  7. The Second Conference on the Lunar Highlands Crust and New Directions. Phosphate-halogen metasomatism of lunar granulite 79215: Impact-induced fractionation of volatiles and incompatible elements
  8. The Second Conference on the Lunar Highlands Crust and New Directions. Reflectance spectroscopy of plagioclase-dominated mineral mixtures: Implications for characterizing lunar anorthosites remotely
  9. The Second Conference on the Lunar Highlands Crust and New Directions. The distribution of Mg-spinel across the Moon and constraints on crustal origin
  10. The occurrence and composition of chevkinite-(Ce) and perrierite-(Ce) in tholeiitic intrusive rocks and lunar mare basalt
  11. Garnet as a major carrier of the Y and REE in the granitic rocks: An example from the layered anorogenic granite in the Brno Batholith, Czech Republic
  12. Mid-infrared optical constants of clinopyroxene and orthoclase derived from oriented single-crystal reflectance spectra
  13. Time-resolved synchrotron X-ray diffraction study of the dehydration behavior of chalcophanite
  14. Ab initio investigations of dioctahedral interlayer-deficient mica: Modeling particles of illite found within gas shale
  15. Trona at extreme conditions: A pollutant-sequestering material at high pressures and low temperatures
  16. In-situ U-Th/Pb geochronology of (urano)thorite
  17. Temperature-induced amorphization of Na-zeolite A: A view from multi-nuclear high-resolution solid-state NMR
  18. “Silicified” pyrochlore from nepheline syenite (mariupolite) of the Mariupol Massif, SE Ukraine: A new insight into the role of silicon in the pyrochlore structure
  19. Physio-chemical properties of gamma-irradiated vermiculite and their significance for radiation protection and thermoluminescence
  20. Ti resetting in quartz during dynamic recrystallization: Mechanisms and significance
  21. Thermodynamic study of monoclinic pyrrhotite in equilibrium with pyrite in the Ag-Fe-S system by solid-state electrochemical cell technique
  22. Phase diagram and P-V-T equation of state of Al-bearing seifertite at lowermost mantle conditions
  23. Crystal structure of Guinier-Preston zones in orthopyroxene: Z-contrast imaging and ab inito study
  24. Crystal chemistry and surface configurations of two polylithionite-1M crystals
  25. Crystal chemistry of synthetic Ti-Mg-bearing hibonites: A single-crystal X-ray study
  26. Mineralogy and crystal chemistry of Mn, Fe, Co, Ni, and Cu in a deep-sea Pacific polymetallic nodule
  27. Agakhanovite-(Y), ideally (YCa)⃞2KBe3Si12O30, a new milarite-group mineral from the Heftetjern pegmatite, Tørdal, Southern Norway: Description and crystal structure
  28. Actinides in Geology, Energy, and the Environment. Ichnusaite, Th(MoO4)2·3H2O, the first natural thorium molybdate: Occurrence, description, and crystal structure
  29. Actinides in Geology, Energy, and the Environment. Quantification of α-particle radiation damage in zircon
  30. What Lurks in the Martian Rocks and Soil? Investigations of Sulfates, Phosphates, and Perchlorates. Spectral properties of Ca-sulfates: Gypsum, bassanite, and anhydrite
  31. What Lurks in the Martian Rocks and Soil? Investigations of Sulfates, Phosphates, and Perchlorates. Flower-like apatite recording microbial processes through deep geological time and its implication to the search for mineral records of life on Mars
  32. What Lurks in the martian Rocks and Soil? Investigations of Sulfates, Phosphates, and Perchlorates. Gypsum in modern Kamchatka volcanic hot springs and the Lower Cambrian black shale: Applied to the microbial-mediated precipitation of sulfates on Mars
  33. Letter. Identification of hydrogen defects linked to boron substitution in synthetic forsterite and natural olivine
  34. Letter. Densified glasses as structural proxies for high-pressure melts: Configurational compressibility of silicate melts retained in quenched and decompressed glasses
  35. Letter. Geobarometry from host-inclusion systems: The role of elastic relaxation
  36. New Mineral Names
  37. Book Review
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