Graeme J. Francolini | Searcharxiv

arXiv2026

Correlative Microstructural Analysis of a Weathered Nantan Meteorite Fragment

The weathering of iron-rich phases within meteorites is a process that significantly alters the microstructure and chemical composition based on the environmental conditions at the location of landing and exposure time since fall. This work investigates the resulting phases in a correlative and comparative manner using a Nantan meteorite fragment. Techniques including X-ray Photoelectron Spectroscopy, Energy Dispersive X-ray Spectroscopy, and X-ray Fluorescence Spectroscopy were used for compositional determination and X-ray Diffraction and Electron Backscatter Diffraction for phase determination and microstructural analysis. These techniques revealed the meteorite matrix to be predominantly composed of magnetite, with distinct regions of high Ni content. The grain size was found to be approximately 5 $μ$m in $\geq$ 2.6 at$\%$ Ni content regions with a visible boundary of 100-200 $μ$m extending into $\leq$ 0.9 at$\%$ Ni regions, wherein the grain size averaged 10s of $μ$m. Additionally, a brecciated cohenite phase was found with a vein-line structure, composed of NiO, magnetite, and deposits of iron and nickel carbonates. This indicates that the matrix regions formed through the weathering of discrete primary phases, with the high Ni regions forming from aqueous alteration of kamacite and the low Ni regions forming from direct dissolution and oxidation of the source Fe-Ni metal.

physics.geo-ph↗

arXiv2025

Microstructural characterization to reveal evidence of shock deformation in a Campo del Cielo meteorite fragment

The study of meteorites and their microstructures is a topic which spans multiple fields of research, such as meteoritics and materials science. For materials scientists and engineers, the extreme and unusual conditions which these microstructures form allow for insight into materials which would exist at the edge of our thermomechanical processing abilities. One such microstructure found in low-shock event iron meteorites is Neumann bands. These bands are an array of lenticular deformation twins that form throughout the Fe-Ni matrix with numerous intersections, resulting in many high stress and strain regions within the material's surface. The existence of these regions and the shocks that formed them encourage atypical strain accommodating mechanisms and structural changes of the material. However, direct investigation of the deformation twin intersections and the microstructural behaviour in and around these regions has been limited. In this work, investigation of these regions in a Campo del Cielo meteorite fragment, with electron backscatter diffraction (EBSD) and forescatter electron (FSE) imaging, revealed two primary findings: high-intensity pattern doubling mirrored across the {110} band at twin-twin intersection and microband formation across the sample surface, which suggest multilayer twinning and constraint of the crystal structure at points of twin-twin intersection. Microbands were found to form along the {110} plane and in regions near Neumann bands. The simultaneous existence of Neumann bands (microtwins) and microbands is presented here for a BCC material, and it is believed the Neumann band and microbands formed during different types and/or shock events. The presence of both Neumann bands and microbands within a BCC iron meteorite is previously unreported and may be valuable in furthering our understanding of shock deformation within iron-based materials.

cond-mat.mtrl-sci↗