The todorokite–buserite problem: further considerations

Todorokite has been shown in several recent HRTEM studies to have a tunnel structure analogous to that of romanechite (psilomelane). Further examinations of the structures and crystal chemistry of romanechite and todorokite suggest that lower valence Mn cations occupy larger M2-type [MnO₆] octahedra constituting the “walls” of the tunnels, which are distorted as a result of the Jahn–Teller effect in Mn³⁺ ions. Atomic substitution of Mg²⁺, Ni²⁺, Cu²⁺, Co²⁺, and Zn²⁺ ions for lower valence Mn cations occur in M2-type sites of todorokite, accounting for the enrichment of Ni, Cu, etc., in many deep-sea manganese nodule deposits. Recent literature is reviewed which identifies asbolan and mixed-layer asbolan–buserite assemblages as additional 10Å manganese (IV) oxide phases occurring in seafloor sediments.