A series of experiments have been carried out to determine which types of ultramafic rocks are most suitable as a feed material for CCSM, using acid leach as the method to remove Mg cations from the rock to be available for carbonation.The results show that lizardite serpentinites are by far the best with olivine giving moderate results. Rocks rich in antigorite serpentine, pyroxene, and amphibole are not suitable.The ETI is grateful for the contributions made by all participants of the Mineralisation project; Perkins Engines Company Limited, Shell Global Solutions International B.V., Natural Environment Research Council as represented by the British Geological Survey, and the University of Nottingham.