Abstract: Thermal phase-transformation of calcium carbonate in samples of pearl powder and conch powder was studied by high-temperature X-ray diffraction (XRD). It was shown that different rate of phase-transformation from aragonite to calcite was observed with both the two samples as the testing temperature was raised; and the content of calcite (w%) in conch powder was increased from 0.5% to 25.5%, while the content of calcite (w%) in pearl powder was increased from 5.0% to 8.1%, under testing temperature of 330 ℃. Considering the result of testing for the temperature and various other factors influential to the analytical result, the temperature of 330 ℃ was chosen in XRD analysis. The phase transformation of the 2 crystalline structures mentioned above in several samples of mixtures of pearl powder and conch powder in various mixing ratios was also studied, and it was found that, linear relationship was kept between the contents (w%) of calcite in the samples and the amount (w%) of conch powder present in the samples, showing that the mechanism of phase transformation was not changed in the mixed powder samples. Under the same experimental condition, rate of the phase-transformation for pearl powder sample was significantly lower than that for conch powder sample. Based on these facts, by application of high-temperature XRD, samples of pearl powder and conch powder can be discriminated accurately and rapidly.