Insights into the direct carbonation of activated lizardite: The identification a poorly reactive amorphous Mg-rich silicate phase

•Two amorphous Mg-rich silicate phases have been identified upon activation.•A highly-reactive amorphous phase nourished the growth of carbonates.•A poorly-reactive phase might explain the low direct carbonation efficiencies.•Magnesite formation occurs when hydromagnesite formation reached a steady state.