CO2 distribution in M-12 and M-14 cages of CO2-rich melanophlogite from Fortunillo, Tuscany, Italy was studied using synchrotron powder X-ray diffraction. Original and two heat-treated samples at 500 and 1000 degrees C were studied at room temperature. The diffraction patterns of these samples can be indexed as a cubic cell (Pm (3) over barn). For the non-heated sample, CO2 occupancy for M-14 cage is close to unity, whereas about 0.85 for M-12 cage. For the 500 degrees C heated sample, the occupancies for M-14 and M-12 cages are reduced to 0.79 and 0.57, respectively. Present study showed that CO2 has preference to M-14 cage, but substantial CO2 occupies M-12 cage. The electron distributions obtained by MEM analysis clearly reveal orientationally ordered CO2 distribution in M-12 and M-14 cages. Present result is also used to clarify a recently proposed interpretation for the splitting of CO2 Raman vibrational peak for the heat-treated melanophlogite.