Pyrolusite tunnel structure

Most Mn(in, IV) minerals have crystal structures that fall into one of three major groups Chain, tunnel, and layer structures (22-24). The chain structures consist of cross-linked single or double rows of MnO octahedra running parallel to the c axis (e.g., pyrolusite). The tunneled structures are formed from two or more cross-linked... 

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.

The crystal structure of pyrolusite, or f -Mn02, is the simplest one within the family of compounds with tunnel structures. The manganese atoms occupy half of the octahedral voids in the hexagonal close packing of oxygen atoms in an ordered manner, thus forming a rutile-type structure. The distorted MnOg units build... 

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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