“…The size of the tunnels, defined by the number of chains, accommodates large cations (e.g., Mg 2+ , Ca 2+ , Ba 2+ , Na + , K + ) and water molecules [ [112] , [113] , [114] , [115] ]. Commonly found tunnel-structured Mn oxide minerals in nature include pyrolusite (1 × 1 configuration), Ramsdellite (1 × 2), nsutite (mixture of 1 × 1 and 1 × 2), cryptomelan (2 × 2), romanechite (2 × 3), and todorokite (3 × 3), with the rare occurrence of woodruffite (3 × 4) [ [116] , [117] , [118] , [119] , [120] , [121] , [122] ]. Under specific conditions in soil or sediments, layered Mn oxides can undergo a transformation into tunnel-structured Mn oxides [ 18 , 37 , 102 , 103 , 123 ].…”