We report the use of gas sorption experiments and in situ powder X-ray diffraction to study the use of dolomite (MgCa(CO3)2) as a potential reversible high-temperature CO2 sorbent. When dolomite is treated in inert atmosphere at 900 degrees C it decomposes into separate CaO and MgO rich phases and dolomite is never reformed pon CO2 sorption. Gas sorption studies show that the calcined dolomite can go through several cycles of CO2 sorption/desorption in a reversible manner, however, the sorption capacity diminishes with each cycle. Only calcium seems to be involved in the CO2 sorption, while MgO acts as a carrier for the calcium phase. Some evidence of magnesium contamination of the calcium phase was found. BET and SEM measurements were carried out to find differences in the surface area/particle morphology that may explain similarities in the sorption capacities of dolomite and calcite (CaCO3).