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Manganese oxides(Mn oxides)are highly reactive mineral phases that play important roles in elemental biogeochemical cycles.Oxidation of soluble Mn(Ⅱ)to insoluble Mn(Ⅲ,Ⅳ)oxide minerals,although thermodynamically favored,tends to be slow in natural environments.Microorganisms catalyze Mn oxidation and increase the reaction rate by several orders of magnitude relative to abiotic reactions.Therefore,envirormental Mn oxides are presumed to be of biological origin.