•A simple carbonization method was developed to synthesize rod-like aragonite from dolomite.•The influences of carbonization factors on the morphology and polymorph of CaCO3 were investigated using SEM and XRD.•The aragonite was obtained at 25 °C by carbonization for 0.5 h without any additives and aging for 12 h.•Aragonite rods have a length of 2.5–3 μm, a width of 0.3–0.4 μm, and an aspect ratio of 6–10.•The mechanism of the phase transformation from calcite to aragonite is also discussed.A simple carbonization method was developed to synthesize rod-like aragonite in CaCl2-NH4Cl solution prepared from dolomite. Scanning electron microscopy and X-ray diffraction were used to characterize the morphology and crystal structure of the aragonite produced. The influences of carbonization time and temperature and aging time on the morphology and polymorph of the precipitated CaCO3 particles were investigated. The aragonite was obtained at room temperature by carbonization for 0.5 h without any additives and aging for 12 h. Aragonite rods with a length of 2.5–3 μm, a width of 0.3–0.4 μm, and an aspect ratio of 6–10 can be synthesized. The mechanism of the phase transformation from calcite to aragonite is also discussed.