|
|||||
|
|
X-ray Spectromicroscopy of Mineral Intergrowths in the Santa Catharina Meteorite |
|
| Authors: | Paul F. Schofield Andrew D. Smith J. Frederick W. Mosselmans Hendrik Ohldag Andreas Scholl Simone Raoux Gordon Cressey Barbara A. Cressey Paul D. Quinn Caroline A. Kirk Simon C. Hogg |
| Affiliation: | 1. STFC Daresbury Laboratory, Daresbury, Warrington WA4 4AD, UK;2. Diamond Light Source Ltd, Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK;3. Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA Present address: Stanford Synchrotron Radiation Laboratory, 2575 Sandhill Road, Menlo Park, CA 94025, USA;4. Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA;5. Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA Present address: IBM T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598, USA;6. Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK;7. Science and Engineering Electron Microscopy Centre, Department of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK;8. Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK Present address: Department of Chemistry, Loughborough University, Loughborough LE11 3TU, UK;9. Department of Materials, Loughborough University, Loughborough LE11 3TU, UK |
| Abstract: | This work describes the application of microfocus X-ray absorption spectroscopy (XAS) and X-ray photo-emission electron microscopy (XPEEM) to the study of the complex mineralogical intergrowths within the Santa Catharina meteorite. The Santa Catharina meteorite of this study (BM52283 from the meteorite collection of the Natural History Museum, London, UK) primarily comprises a taenite bulk host phase (Fe:Ni ratio = 70.9 ± 0.8%:29.1 ± 0.8%) with a set of oxide-bearing cloudy zone textured regions (Fe:Ni:O ratio = 40.4 ± 0.3%:49.0 ± 0.7%:10.6 ± 0.8% at the core and Fe:Ni:O ratio = 34.4 ± 1.5%:42.7 ± 0.6%:22.9 ± 1.8% towards the rims) and numerous schreibersite (Fe:Ni:P ratio = 38.6 ± 1.6%:38.4 ± 0.9%:23.0 ± 0.5%) inclusions. Between the schreibersite and the taenite are rims up to 50 μm across of Ni-rich kamacite (Fe:Ni ratio = 93.4 ± 0.4%:6.6 ± 0.5%). No chemical zoning or spatial variations in the Fe and Ni speciation was observed within either the schreibersite or the kamacite phases. The oxide-bearing cloudy zone textured regions mostly comprise metallic Fe–Ni alloy, predominantly tetrataenite. Within the oxide phases, the Fe is predominantly, but not entirely, tetrahedrally co-ordinated Fe3+ and the Ni is octahedrally co-ordinated Ni2+. Structural analysis supports the suggestion that non-stoichiometric Fe2NiO4 trevorite is the oxide phase. The trevorite:tetrataenite ratio increases at the edges of the oxide-bearing cloudy zone textured regions indicating increased oxidation at the edges of these zones. The spatial resolution of the XPEEM achieved was between 110 and 150 nm, which precluded the study of either the previously reported ∼ 10 nm precipitates of tetrataenite within the bulk taenite or any antitaenite. |
| Keywords: | Santa Catharina meteorite antitaenite X-ray photo-emission electron microscopy XPEEM microfocus X-ray spectroscopy non-destructive analysis Météorite Santa Catharina antitaenite microscopie électronique à photo-émission de rayons X XPEEM spectrométrie d’absorption des rayons X microfocalisée analyse non-destructive |