Abstract: | During investigations of the formation of hydrated magnesium carbonates, a sample of the previously unknown magnesium carbonate hexahydrate (MgCO3·6H2O) was synthesized in an aqueous solution at 273.15 K. The crystal structure consists of edge‐linked isolated pairs of Mg(CO3)(H2O)4 octahedra and noncoordinating water molecules, and exhibits similarities to NiCO3·5.5H2O (hellyerite). The recorded X‐ray diffraction pattern and the Raman spectra confirmed the formation of a new phase and its transformation to magnesium carbonate trihydrate (MgCO3·3H2O) at room temperature. |