The Miller 03356 IVA iron: Insights into the formation mechanism of microplessite

D. Ray, S. Ghosh, M. Paliwal, S. Mishra, J. Jha

Planetary and Space Science
In Press, Journal Pre-proof, Available online 19 December 2022


“The Miller 03356, IVA iron was earlier reported as a fragment of ‘Plessitic Octahedrite’, IVA iron with α2 microstructures and Neumann bands. Our investigations report a couple of primary textures and microtextures ranging from Widmanstätten pattern to finger plessites, cellular plessites, duplex plessites, and finally optically unresolvable black plessites where decomposed martensite (α2) laths retain micro Widmanstätten pattern. In black plessites exsolved taenite precipitates are aligned along the α2-lath boundaries whereas the taenite precipitates within the retained α2-laths show varying orientations. The electron back-scattering diffraction pole diagrams show normal bcc-fcc orientation relationships for fine textured black plessites that substantiate the ideal Kurdjumov-Sachs (K–S) relationships in crystal lattice scale; on contrary, more than a single orientation of parent taenite phase was involved in the transformation to bcc martensite in coarse-textured duplex plessites. Neumann bands in kamacites, incipient development of ɛ-kamacites, and selective polygonisation of kamacites trace back the history of one mild and one moderate impact due to compressive shock pressure between 2 GPa and 13 GPa and post-shock reheating between 800 °C and 1000 °C.”