Psilomelane, tunnel structures

Figure 2. Representation of the Psilomelane structure (treble chains of MnO6 octahedra joined to double chains of same, resulting in extended tunnel structure) of manganese dioxide. In aqueous media the terminal groups may have coordinated H2O or OH (or their dissociated equivalents, OH- or O ) present.

Figure 7. Crystal structures of (a) hollandite, (b) romanechite (psilomelane), and (c) todorokite. The structures arc shown as three-dimensional arrangements of the MnO() octahedra (the tunnel-tilling cations and water molecules, respectively, are not shown in these plots) and as projections along the short axis. Small, medium, and large circles represenl the manganese atoms, oxygen atoms, and the foreign cations or water molecules, respectively. Open circles, height z. = 0 fdled circles, height z = Vi.

The crystal structure of romanechite (or psilomelane) is closely related to that of a-MnO,. Where as the or-modification of manganese dioxide consists of cornersharing double chains of MnO octahedra connected trough common edges, the romanechite structure is build up by crosslinking of chains of double and triple octahedra, as shown in Fig. 7(b). The resulting [2 X 3] tunnels, extending in the h direction of the monoclinic cell, are partially... 

Figure 3.7 Crystal structures of (a) hollandite, (b) romanechite (psilomelane), and (c) todorokite. The structures are shown as three-dimensional arrangements of the MnOe octahedra (the tunnel-filling cations and water molecules, respectively, are not...

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