Addition of potassium carbonate solution to zinc acetate solution at room temperature causes the precipitation of a white solid, whose composition and structure depend on the initial concentrations of the reagents. Hydrozincite, Zn-5(CO3)(2)(OH)(6), forms when the K2CO3 concentration is low and a new K-containing zinc carbonate hydroxide phase forms when the K2CO3 concentration is high. The chemical formula of the new phase has been determined to be Zn(CO3)(0.61)(OH)(0.78)(.)0.233K(2)CO(3) by TGA, CHNO and AA analysis. The new phase is insoluble in water and extensive water washing of the new phase does not change its composition or structure, suggesting the new phase is a single phase compound salt. Exposure of the new phase to a stream of humidified CO2 causes disproportionation to separate phases of ZnCO3 and K2CO3. Pure ZnCO3 was synthesized for comparison by a new procedure under atmospheric conditions instead of the more common hydrothermal synthesis of ZnCO3. (C) 2004 Elsevier Ltd. All rights reserved.