Evidence of a hydrated mineral enriched in water and ammonium molecules in the Chang’e-5 lunar sample

The presence and distribution of water on the Moon are fundamental to our understanding of the Earth–Moon system. Despite extensive laboratory research and remote sensing explorations, the origin and chemical form of lunar water have remained elusive. In this study we present the discovery of a hydrated mineral, (NH)MgCl·6HO, in lunar soil samples returned by the Chang’e-5 mission that contains approximately 41 wt% HO. The mineral’s structure and composition closely resemble novograblenovite, a terrestrial fumarole mineral formed through the reaction of hot basalt with water-rich volcanic gases, and carnallite, an Earth evaporite mineral. We rule out terrestrial contamination or rocket exhaust as the origin of this hydrate on the basis of its chemical and isotopic compositions and formation conditions. The presence of ammonium indicates a more complex lunar degassing history and highlights its potential as a resource for lunar habitation. Our findings also suggest that water molecules can persist in sunlit areas of the Moon as hydrated salts, providing crucial constraints on the fugacity of water and ammonia vapour in lunar volcanic gases.