Structure and occurrences of ≪ green rust ≫ related new minerals of the ≪ fougérite ≫ group, trébeurdenite and mössbauerite , belonging to the ≪ hydrotalcite ≫ supergroup; how Mössbauer spectroscopy helps XRD.

Mössbauer spectroscopy yields decisive information for interpreting x-ray diffraction (XRD) patterns in the case of ‘green rusts” with intercalated CO _3^2- anions, i.e. the chemical analogs of the three minerals that constitute within the ≪ hydrotalcite ≫ supergroup comprising 44 minerals the “ fougèrite ” group where the structure stays globally unchanged. The only difference comes from the deprotonation of OH − ions at the apices of the octahedrons occupied by the Fe cations so that Fe I I ions become Fe I I I . Low angle x-ray diffraction using synchrotron radiation displays the presence of many polytypes which reflects the stacking of brucite like layers and anion interlayers so that a 2D long range order of anions stays unchanged from fougèrite to mössbauerite .