Ramsdellite, tunnel structures

Fig. 7.4 Tunnel structures based on rutiles, (a) Rutile-like chains, showing alternately short and long metal-metal distances, as in MoOj. (h)-(

Generally, there are two major structural forms for these minerals chain or tunnel structures, and layer structures. All of these forms are comprised of MnOs octahedras. Water molecules and/or other cations (8) are ofien present at various sites in the structures. Mn oxides having a chain or tunnel structure include pyrolusite, ramsdellite, hollandite, romanechite, and todorokite. Typical structures for the chain or tunnel type Mn oxide mineral are presented in Figure 1. Lithiophorite, chalcophanite, and bimessite are examples of Mn oxide minerals havii a layer structure. Typical structural maps are shown in Figure 2. 

Figure 1. Polyhedral representations of crystal structures of Mn oxide minerals with chain or tunnel structures. (A) Pyrolusite. (B) Ramsdellite.

Fig. 6.2 Schematic view of the tunnel structure of Mn02 polymorph (a) pyrolusite p-Mn02 (Ti i) and (b) ramsdellite R-Mn02 (Tj 2), hollandite a-Mn02 (T2,2) and (c) nsutite y-Mn02 (intergrowth Ti.i + Ti 2)...

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