The sulfation and steam hydration reactivation characteristics of nine limestones were evaluated based on laboratory sulfation and hydration rests and scanning electron microscope analyses. The calcium utilization and the sulfation pattern of the limestones were found to depend on the morphology and microstructure of the calcined limestones. Three sulfation patterns were observed in the limestones: unreacted core, uniformly sulfated and network. The steam hydration behavior of the sulfated limestones was dependent on the sulfation pattern. Unreacted core particles appeared to be easier to reactivate, thereby giving higher overall calcium utilization, compared to network-sulfated particles. Uniformly sulfated particles did not react upon hydration and could not be reactivated with steam at 250 or 450 degrees C.