A relationship between d104 value and composition in the calcite-disordered dolomite solid-solution series

X-ray diffraction has been widely used in analyzing Ca-Mg carbonates. Compositions of biogenic and inorganic (Ca,Mg)CO 3 crystals are often calculated by comparing their d 104 values with published empirical curves. However, previous studies suggested that these curves do not apply to very high-Mg calcite and disordered dolomite. Based on synthesized high-Mg calcite and disordered dolomite, a new empirical curve between values of magnesian calcite d 104 and MgCO 3 content in the calcite-disordered dolomite solid-solution series is constructed. This new curve is consistent with the significant cell parameter changes accompanying the Mg-Ca cation disorder in dolomite, and it can help the characterization of the MgCO 3 content of both natural and synthetic magnesian calcite and disordered dolomite, especially for the mineral mixtures that are not suitable for other analysis methods.