Members of norsethite-type carbonate solid solutions with the compositions Ba(Mg1–xMnx)(CO3)2, (x = 0, 0.25, 0.50 and 0.75) have been synthesised under high-pressure and -temperature conditions (3GPa, 800°C) for the first time. The synthetic transparent crystals gradually changed their appearance from colourless to blue lustre with the increasing Mn2+ content (XMn). The results of the crystal structure analyses reveal that the lattice parameters (a, c, unit-cell volume, Mg/Mn–O bond lengths and Ba–O bond lengths) complied with a linear increase with XMn. In contrast, the C–O bond lengths and O–C–O bond angles decreased, because the CO32– group was squeezed by the expansion of the (Mg/Mn)O6 octahedra. Moreover, the Raman and infrared vibrations, except for the lattice mode T, shift to low frequency with the increasing XMn, and the slight corresponding variations of the atomic positions were also determined. These new results demonstrate the impact of Mg2+–Mn2+ substitution on the crystal chemistry of norsethite-type solid solutions, with further implications for the natural occurrence and environmental of norsethite-type and dolomite/ankerite-type carbonates.