From the viewpoints of energy and environmental problems in the world, development of chemical heat pump technology and its practical uses are required. A chemical heat pump using a reversible calcium oxide/water reaction system has been proposed to promote thermal energy utilization. In this report three CaCO3 materials, namely, lime, scallop and coral powder, were examined on the reactivity of the hydration/dehydration of CaO/Ca(OH)(2) and the possibility of scallop and coral as the alternates of limestone was discussed. CaO particles used as a reactant were prepared by the calcination of the three CaCO3 materials. The difference of the CaCO3 resource in the hydration and the dehydration reactivity of the CaO/Ca(OH)(2) system was studied by the use of a closed system reactor with forced convection. The compositions of the lime, coral and scallop powder were almost the same, while hydration conversions of the three materials were different from each other. Especially the reactivity of the scallop powder was considerably low in comparison with the other two materials. However, the difference among these hydration conversions disappeared by the repetition of hydration/dehydration reactions. The hydration conversions of three materials prepared by the repetition of reactions agreed well with one calculated by a model proposed by the authors. CaO made from the scallop with reaction repetition has almost as high a reaction capacity as CaO made by calcination of lime and coral.