Carbonated wollastonite is a potential novel supplementary cementitious material. Because of the limited natural reserves only industrially manufactured wollastonite, which can be produced in conventional cement kilns from limestone and a silica source, emitting 30% less CO2 than PC clinker, is of global interest. Upon carbonation, a silica-rich amorphous phase and calcite form. In blends with Portland cement, early hydration is accelerated, and the silica-rich amorphous phase shows a pozzolanic reaction. This participation in the cement hydration reactions leads to a positive contribution to compressive strength.