Chalcophanite, structure

Similarly to Mn,Ox and related compounds, the chalcophanite structure can be interpreted as a filled Cdl2-type structure. The space in the octahedral layer is filled by an additional layer of water molecules and some foreign cations. A comparable situation is found in several hy-droxozincates, e.g., Zn5(OH)8Cl2 H20 or Zn5(OH)6(CO)3. In these compounds the layers are formed by edge-sharing zinc hydroxide octahedra, Zn(OH)6, and the space between the layers is filled with chloride and carbonate anions and some Zn2+ cations, which are located above and below vacancies in the Zn - OH layers. 

The crystal structure of the mineral chalcophanite, ZnMn307-3H20 (see Fig. II), was one of the first layer structures of manganese oxides that has been determined. 

Figure 8.8 Structure of chalcophanite, a Mn(IV) oxide with a layer structure, (a) Projection along the b axis showing layers of [MnOg] octahedra linked by Zn octahedra. (b) The edge-shared [MnOfi] octahedral layer viewed normal to the basal plane. The vacant octahedral sites at the origin are at the comers of a rhombus outlining the plane of Mn atoms. Note that one out of seven Mn positions is vacant, so that each Mn is...

Post, J. E. Appleman, D. E. (1988) Chalcophanite, ZnMn307.3H20 New crystal-structure determination. Amer. Mineral., 73, 1401-4. 

Wadsley AD (1952) The structure of lithiophorite, (Al,Li)Mn02(0H)2. Acta Cryst 5 676-680 Wadsley AD (1955) The crystal structure of chalcophanite, ZnMn307.3H20. Acta Cryst 8 1165-1172 Wasserman SR, Allen PG, Shuh DK, Bucher JJ, Edelstein NM (1999) EXAFS and principal component... 

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 2. Polyhedral representations of crystal structures ofMn oxide minerals with layer structures. (A) Lithiophorite. (B) Chalcophanite. (C) Na-rich bimessite-like phase showing disordered H20/Na (light color ball) sandwiched between the Mn octahedral sheets. Adapted from (8).

Figure 11. Projection of the chalcophanite (ZnMniO, OHjO) structure along the crystallographic h-uxis. The structure consists of layers of edge-sharing MnOf, octahedra, a separating water layer and single zinc ions which are octahedrally coordinated by three oxygen atoms from the Mn - O sheets and three oxygen atoms from the water layer.

Figure 3.11 Projection of the chalcophanite (ZnMn307-3H20) structure along the crystallographic b-axis. The structure consists of layers or edge-sharing MnOe octahedra, a...

Associated with each Mn-O layer and directly above and below the unoccupied Mn position, the Zn ions are located in a somewhat distorted octahedral void, formed by three oxygen atoms of the Mn-O layer and three oxygen atoms from the water layer. The two kinds of sheets in the structure are held together by H-O bridging bonds between the water molecules and the oxygen atoms of the Mn-O layer. Natural chalcophanites differ quite significantly from the ideal composition. 

Post and Veblen [65] investigated the crystal structures of several synthetic sodium, potassium, and magnesium bimessites by electron diffraction methods and Rietveld refinements of XRD patterns. Starting from the crystal structure of chalcophanite they determined the atomic arrangement in these compounds. The materials of the composition A,cMn02-yH20 (A = Na, K, Mg) have monochnic symmetry (see Table 3.3). Post and Veblen reported a number of detailed structural... 

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