Hydroxysulphate green rust GR(SO{4/2-}) species were precipitated in the presence of various anions. GR(SO{4/2-}) is stable at ˜pH 7 and is transformed into a mixture of magnetite and ferrous hydroxide when the pH raised at ˜12. In the presence of carbonate species, GR(SO{4/2-}) is partially transformed into a mixture of magnetite and siderite at ˜pH 8.5. This transformation is stopped when silicate anions are present in the solution. As already observed for phosphate anions, the adsorption of silicate anions on the lateral faces of the GR(SO{4/2-}) crystals may explain this stabilization effect. Sulphate anions are easily exchanged by carbonate species at ˜pH 10.5. In contrast, anionic exchange between sulphate and phosphate anions was not observed.