Abstract The transformation of olivine during the conversion of CO 2 to light hydrocarbons activated by mechanochemical treatments at different impact frequencies was studied by a combination of several complementary characterization methods including X-ray diffraction, Raman and 57 Fe Mössbauer spectroscopy. Several olivine samples were studied as a function of the milling time, indicating the gradual transformation of Fe II -containing olivine into new Fe III -containing weathering products including iron oxides, magnesium iron carbonates and silicates. The results presented here complement those of a previous study on the weathering process of olivine promoted by mechanochemical activation, by demonstrating the role of the redox activity of the iron species during the activation process. These additional spectroscopic results allow us to thoroughly understand the complex weathering mechanism and to correlate it with the efficiency of the CO 2 conversion and storage properties of mechanochemically activated olivine.