X-ray Spectromicroscopy of Mineral Intergrowths in the Santa Catharina Meteorite

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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 mu m 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 Fe(2)NiO(4) 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 similar to 10 nm precipitates of tetrataenite within the bulk taenite or any antitaenite.Ce travail decrit l'application des techniques de spectrometrie d'absorption des rayons X microfocalisee (XAS) et de microscopie electronique a photo-emission de rayons X (XPEEM) a l'etude de la mineralogie complexe des intercroissances de la meteorite de Santa Catharina. La meteorite de Santa Catharina de cette etude (BM52283 de la collection de meteorites du Museum d'Histoire Naturelle, Londres, Royaume-Uni) comprend essentiellement une taenite comme phase minerale hote (proportions de Fe:Ni = 70.9 +/- 0.8%:29.1 +/- 0.8%) avec un ensemble de regions caracterisees par des zones nuageuses contenant des oxydes (proportions de Fe:Ni:O = 40.4 +/- 0.3%:49.0 +/- 0.7%:10.6 +/- 0.8% au niveau des coeurs et de 34.4 +/- 1.5%:42.7 +/- 0.6%:22.9 +/- 1.8% vers les bords) et de nombreuses inclusions de schreibersite (Fe:Ni:P = 38.6 +/- 1.6%:38.4 +/- 0.9%:23.0 +/- 0.5%). Entre la schreibersite et la taenite des bords de kamacite riche en Ni d'un diametre pouvant atteindre 50 micrometres s'observent (proportions de Fe:Ni = 93.4 +/- 0.4%:6.6 +/- 0.5%). Aucun zonage chimique et aucune variation spatiale de la speciation de Fe et Ni n'ont ete observes dans les schreibersites et dans les kamacites. Les regions caracterisees par des zones nuageuses a oxydes contiennent essentiellement des alliages metalliques de Fe-Ni, surtout de la tetrataenite. Dans les oxydes le Fe est principalement, mais pas entierement, en coordinence tetraedrique Fe3+ et le Ni en coordinence octaedrique Ni2+. L'analyse structurale appuie la suggestion que la trevorite Fe(2)NiO(4) non stoechiometrique est la phase oxyde.

Le rapport trevorite/tetrataenite augmente au nivea des bords des regions caracterisees par des zones nuageuses a oxydes indiquant une augmentation du niveau d'oxydation au niveau des bords de ces zones. La resolution spatiale atteinte pour l'XPEEM se situait entre 110 et 150 nm, ce qui a empeche l'etude des precipites de tetrataenite precedemment signales et d'une taille d'environ 10 nm ainsi que de toute antitaenite.

Original languageEnglish
Pages (from-to)145-159
Number of pages15
JournalGeostandards and Geoanalytical Research
Volume34
Issue number2
DOIs
Publication statusPublished - Jun 2010

Keywords

  • Santa Catharina meteorite
  • antitaenite
  • X-ray photo-emission electron microscopy
  • XPEEM
  • microfocus X-ray spectroscopy
  • non-destructive analysis
  • Meteorite Santa Catharina
  • microscopie electronique a photo-emission de rayons X
  • spectrometrie d'absorption des rayons X microfocalisee
  • analyse non-destructive
  • PHOTOEMISSION ELECTRON-MICROSCOPY
  • IRON OXIDATION-STATES
  • 3D TRANSITION-METALS
  • ABSORPTION-SPECTROSCOPY
  • SYNCHROTRON-RADIATION
  • CLOUDY ZONE
  • EDGE
  • PHASES
  • PEEM
  • MICROSPECTROSCOPY

Cite this