Discovery of crystalline Fe₂O₃ in returned lunar soils

Lunar materials were believed to have formed and been preserved in a reducing environment, with only Fe²⁺ and Fe⁰ present. Native oxidized minerals, such as hematite, have not been validated in previously returned lunar samples. In this work, we report the discovery of micrometer-scale crystalline Fe₂O₃ in the forms of hematite (α-Fe₂O₃) and maghemite (γ-Fe₂O₃) overgrowing troilite in the recently returned Chang'e-6 (CE6) lunar soils. It is possible that impact-induced oxygen release created localized micrometer-scale regions of elevated oxygen fugacity, facilitating the formation of Fe₂O₃ at temperatures between ~700° and 1000°C. This finding provides credible evidence for the presence of Fe₂O₃ on the lunar surface, challenging the traditional understanding of lunar surface redox states. In addition, the Fe₂O₃ in the form of maghemite may be the mineralogical reason for the generation of the magnetic anomalies observed around the South Pole-Aitken basin.