Volumetric Analysis and Phase Discrimination in Meteorites by Medical X-Ray Micro-CT

David Edey1,2, Roberta L Flemming3, Steven Pollmann2, Daniel Lorusso2,4, Maria Drangova2,5, Phil J A McCausland6 and David Holdsworth7, (1)Jackson School of Geosciences, University of Texas at Austin, Austin, TX, United States, (2)Robarts Research Institute, Imaging Research Laboratories, London, ON, Canada, (3)University of Western Ontario, Earth Sciences, London, ON, Canada, (4)University of Western Ontario, Schulich School of Medicine and Dentistry, London, ON, Canada, (5)University of Western Ontario, Department of Medical Biophysics, London, ON, Canada, (6)University of Western Ontario, London, ON, Canada, (7)Western University, Robarts Research Institute, London, ON, Canada

Contact First Author: David Edey; dave.edey@utexas.edu

Abstract ID#: 36337

 

English Abstract:
Micro-Computed Tomography (µCT) enables access to spatial compositional and textural information in meteorites, to inform further investigation without the need for destructive analysis. Furthermore, high resolution images of meteorites attained in biomedical micro-CT scanners (GE eXplore Locus and GE eXplore speCZT at Robarts Research Institute) can be quantitative, with applicable correction. We report quantitative estimates for metal plus sulfide in H chondrites, as well as silicate phase discrimination in olivine diogenite, after image correction using a semi-empirical linearization of X-ray projection data using a custom calibration phantom to correct for beam hardening and scatter. Data from four meteorites are compared: Bassikounou H5, Gao-Guenie H5 and Grimbsy H4-5 ordinary chondrites and NWA 5480, a coarse-grained olivine diogenite. The chondrites demonstrated excellent agreement between % volume composition of dense metallic inclusions (metal plus sulfide) from corrected µCT images, as compared to literature values, point counting by reflected light microscopy, and SEM imaging (LEO 440 SEM at Surface Science Western), respectively. Silicate phases could not be discerned in the ordinary chondrites because of their fine-grained nature. By µCT, it is possible to distinguish the mineral phases in coarse-grained NWA 5480 (grains of mm size) using the large contrast between radiodensities of the different phases. The three most abundant phases in NWA 5480, enstatite, forsterite and chromite, as identified spatially by in situ µXRD analysis of the surface (Bruker D8 Discover), could be correlated to distinguishable mineral phases by μCT. Thus for this coarse-grained achondrite, the silicate minerals enstatite and forsterite could be distinguished easily by the lower radiodensity of the former. Medical CT imaging cannot reliably distinguish between sulphide and metal phases (both saturate) nor between silicates except in cases where the sample is coarse-grained.
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