Amorphous silica and hydrated magnesium carbonate (nesquehonite, MgCO3·3H2O) have been produced by acid dissolution of olivine ((Mg,Fe)2·SiO4). The amorphous silica is a viable supplementary cementitious material, and the formation of nesquehonite by carbonation, results in a carbon negative process. Using the amorphous silica as a supplementary cementitious material produces low-carbon cement. The global reserve of olivine makes this a viable route to producing low-carbon concrete.