Thermal decomposition process of dypingite Mg5(CO3)4(OH)2·5H2O

•Dypingite possesses an identical local structure as that of hydromagnesite.•Dypingite transformed to the high-temperature structure until 100 °C, but its local structure remained unchanged.•The local structure of dypingite was hardly changed with temperature, but that of hydromagnesite was readily changeable.•Dypingite crystallized into MgO through the different thermal transformation pathways from hydromagnesite. Dypingite is one of the most common phases of crystalline magnesium carbonate hydrates, which are considered potential targets for CO2 mineral sequestration. Ex-situ high-temperature X-ray diffraction and ex-situ high-temperature synchrotron X-ray scattering experiments with pair distribution function analysis were used to explore the thermal transformation process of dypingite. Dypingite transformed to hydromagnesite until 100 °C, but its local structure remained unchanged. At the temperature range from 250 °C to 350 °C, where the amorphous phase was predominant, the second and third coordination spheres were continuously modified and crystallized to MgO at 400 °C. Although the local structure of dypingite was as that of hydromagnesite, dypingite exhibited a different thermal transformation pathway from hydromagnesite.