Mössbauerite, Fe63+O4(OH)8[CO3]·3H2O, the fully oxidized ‘green rust’ mineral from Mont Saint-Michel Bay, France

Researchers have discovered mössbauerite, a fully oxidized 'green rust' mineral (Fe63+O4(OH)8[CO3]·3H2O), in the intertidal gleys of Mont-Saint-Michel Bay, France. This new mineral, part of the fougèrite group within the hydrotalcite supergroup, represents the highest oxidation state analogue of its group and is characterized by a layered double hydroxide structure with brucite-like layers intercalated with carbonate anions and water molecules. The study utilized electrochemical analysis of synthetic analogues and Mössbauer spectroscopy to identify and characterize mössbauerite, which forms as micrometer-scale platelets under restricted oxygen conditions and rapidly decomposes upon air exposure. Unlike its predecessors, fougèrite and trébeurdenite, pure synthetic mössbauerite is orange in color. The research also revealed that mössbauerite exhibits gradual magnetic ordering below 70-80 K, suggesting short-range coupling of interlayer carbonate anions with octahedral layers while maintaining long-range order.

Génin, J.-M. R., Mills, S. J., Christy, A. G., Guérin, O., Herbillon, A. J., Kuzmann, E., Ona-Nguema, G., Ruby, C., & Upadhyay, C. (2014). Mössbauerite, Fe₆³⁺O₄(OH)₈[CO₃]·3H₂O, the fully oxidized ‘green rust’ mineral from Mont Saint-Michel Bay, France. Mineralogical Magazine, 78(2), 447–465. https://doi.org/10.1180/minmag.2014.078.2.14