[Display omitted] • Facile synthesis of calcite 1D nanoparticles with different Mg2+-doping amount. • In water, nanorods doped with Mg2+ 37,000 ppm or higher were thermally very stable. • In air, nanorods doped with Mg2+ 10,000 ppm or higher were thermally very stable. • STEM observations revealed that Mg-calcite nanoclusters cover the nanorod surfaces. Calcite-core/Mg-calcite (Mg x Ca 1− x CO 3)-shell nanorods were synthesized by bubbling CO 2 gas into Ca(OH) 2 aqueous slurry with Mg2+ doping. The thermal stability of the resulting particles in the forms of aqueous slurry and dry powder was investigated, and the nanorods doped with higher Mg2+ concentrations were found to have excellent thermal stability both in water and air. The microscopic structures of the nanorods were characterized in detail by XRD and TEM, and the Mg-calcite nanoclusters that almost fully covered the particle surface were deduced to be responsible for the improvement of particle morphology stability. Facile fabrication of 1D anisotropic nanoparticles with better thermal stability can widen the industrial application of calcite. [ABSTRACT FROM AUTHOR]