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An X-ray and electron microprobe study of Fe, Ni, Ga, and Ge distribution and local structure in a section of the Canyon Diablo iron meteorite

Ronald G. Cavell^1,2,*, Elspeth M. Barnes², Patricia H. Arboleda^2,, Patricia A. Cavell³, Renfei Feng², Robert A. Gordon⁴ and M. Adam Webb²

¹ Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2
² The Alberta Synchrotron Institute, c/o University of Alberta Research Transition Facility, 8308-114 Street, Suite 2080, Edmonton, Alberta Canada T6G 2E1
³ Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E3
⁴ Pacific Northwest Consortium (PNC-CAT at APS) and Department of Physics, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada, V5A 1S6

Correspondence: ^* E-mail: ron.cavell{at}ualberta.ca

Using X-rays produced by a third generation synchrotron at the Pacific Northwest Consortium Collaborative Access Team (PNC-CAT), Advanced Photon Source (APS), Argonne National Laboratory, the distribution of Fe, Ni, Ga, and Ge in a sample of the Canyon Diablo iron meteorite has been mapped microscopically in situ with a 5 µm x 5 µm spatial resolution. The principal phases investigated were kamacite (Fe/Ni alloy, <6 wt% Ni), cohenite [a carbide, (Fe,Ni,Co)₃C], and schreibersite [a phosphide, (Fe,Ni)₃P]. A non-microscopic X-ray absorption analysis at the P edge indicated the presence of both phosphide and phosphate in the sample. Extended X-ray absorption fine structure (EXAFS) analysis of Fe in kamacite reflects the known bcc structure of kamacite. EXAFS analysis of Ni, Ga, and Ge indicates that these elements substitute for Fe within the kamacite bcc structure. Absorption edge shifts for these same elements are generally small relative to the metals themselves, suggestive of a metallic environment. Initial findings also suggest that Ga preferentially partitions into schreibersite (phosphide) rather than cohenite (carbide), whereas Ge behaves differently and is found principally in the kamacite. These observations further the understanding of the Ge and Ga budget within the Canyon Diablo meteorite, and the work also illustrates the potential of the X-ray microprobe technique for the study of meteorites. Other potential uses of the X-ray microprobe are indicated.