Fire-Induced Thermal Alteration in Iron Meteorites: Metallographic Analysis of the 2018 Disaster at the National Museum of Rio de Janeiro
DOI:
https://doi.org/10.11137/1982-3908_2026_49_71839Keywords:
Fe–Ni alloys, Widmanstätten pattern, Thermal damage classificationAbstract
The fire that destroyed the main building of the National Museum of Rio de Janeiro (MN/UFRJ) on 2 September 2018 exposed one of the largest meteorite collections in the Southern Hemisphere to highly heterogeneous thermal conditions. Iron meteorites stored in different sectors of the building experienced markedly variable thermal stress, ranging from negligible heating to intense reheating beneath collapsed, thermally insulating debris. This study presents a detailed metallographic investigation of iron meteorites from the MN/UFRJ collection, aimed at identifying and characterizing fire-induced thermal alterations, distinguishing them from primary meteoritic features, and establishing a practical framework for damage documentation and classification. Comparative optical microscopy, SEM–EDS analyses, and Ni–P chemical profiling reveal a continuous sequence of diffusion driven microstructural modifications, including attenuation or loss of Neumann bands, recrystallization and fragmentation of kamacite, redistribution of Ni and P at metal interfaces, and partial destabilization of schreibersite. Based on these systematic patterns, a seven-level thermal damage classification (F0–F7) is proposed, correlating observable metallographic features with inferred temperature–time conditions, from pristine Widmanstätten structures to complete melting and resolidification of the metallic mass. The classification scheme is applied to the MN/UFRJ collection and incorporated into specimen records and physical labels, supporting both scientific interpretation and conservation planning. More broadly, the results demonstrate that even short-lived fire exposure can imprint diagnostic and quantifiable overprints on meteoritic microstructures, underscoring the necessity of recognizing and documenting anthropogenic thermal alteration when studying and preserving meteorite collections worldwide.
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