‘Almost Impossible’ Deep-Earth Diamonds Confirm How These Gems Form

South African diamonds containing both oxidized carbonate minerals and reduced nickel alloys reveal how these gems form deep in Earth's mantle. This unprecedented discovery confirms diamonds can form when carbonate fluids from subducting plates react with metal alloys, capturing a snapshot of the reaction midpoint. The findings provide crucial real-world evidence of mantle chemistry between 280-470km deep, suggesting oxidized materials exist deeper than previously thought and potentially explaining the mystery of nickel atoms in diamond structures.