Methods and systems for making calcium oxide (CaO), carbon dioxide (CO2) and/or calcium hydroxide (Ca(OH)2) from aragonite, for example, oolitic aragonite, are provided. The method can include applying solar energy, for example, by focusing one or more mirrors in one or more heliostats, to heat a reactant mixture in a vessel. The reactant mixture includes oolitic aragonite and can be heated to a temperature from 500° C. to 950° C. The system can include a vessel and a means for applying solar energy to heat a supply of oolitic aragonite disposed inside the vessel. Methods of converting the CO2 to ethanol, ethylene, graphene, and/or methane are also provided.