The identification of the fougerite mineral responsible for the bluish-green shade of gleysols in aquifers as being the Fe^{II − III} oxyhydroxycarbonate \textGR(\textCO₃^2-)^*\text{GR}(\text{CO}_{3}^{2-})^* of formula, [\textFe^II_6x\textFe^III_{6(1 - x)}\textO₁₂\textH_2(7-3x)]²⁺·[\textCO₃^2-·3\textH₂\textO]^2-[\text{Fe}^{\rm II}_{6x}\text{Fe}^{\rm III}_{6(1 - x)}\text{O}_{12}\text{H}_{2(7-3x)}]^{2+}\bullet[\text{CO}_{3}^{2-}\bullet3\text{H}_{2}\text{O}]^{2-} where the ferric molar ratio x = [Fe^III/Fe_total] is restricted to the domain [1/3–2/3] induces to study the reactivity of the synthetic green rust for reducing some major pollutants. The oxidation within the solid compound \textGR(\textCO₃^2-)^*\text{GR}(\text{CO}_{3}^{2-})^* in the presence of nitrates is followed by miniaturized Mössbauer spectrometer (MIMOS). Ratio x = [Fe^III/Fe_total] increases up to 0.67 where \textGR(\textCO₃^2-)^*\text{GR}(\text{CO}_{3}^{2-})^* transforms gradually into magnetite. This could well explain the composition variability of fougerite occurrences.