Ramsdellite crystal structure

Bystrom, A. M. (1949) The crystal structure of ramsdellite, an orthorhombic modification of Mn02. Acta Chem. Scand., 3,163-73. 

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

Figure 3.1 Crystal structure of (a) 6-Mn02, (b) ramsdellite, and (c) the intergrowth structure of these two compounds, y-Mn02. The structures are shown as three-dimensional arrangements of the MnOs octahedra and as projections along the short crystallographic...

Ramsdellite is thermodynamically unstable toward a transformation into the stable ft -modification. Hence, it is rarely found in natural deposits. Natural ramsdellite has a stoichiometry close to the composition of Mn02 and can be considered another true modification of manganese dioxide. Attempts to synthesize ramsdellite in the laboratory usually lead to materials of questionable composition and structural classification. It is very likely that synthetic ramsdellite materials are more or less well-crystallized samples of the y-modification that will be described in more detail below. 

The monoxides are known for all of the rare earth metals. They are all crystallizing at low temperatures isostructural to the NaCl-type. EU3O4 crystallizes orthorhombic [45, 46] with space group Pnam. This mixed valent compound contains Eu + and Eu + in the cation sublattice with a distorted octahedral coordination around Eu + and a coordination number of eight around Eu +. Fig. 3-19 shows the projection of the structure down [010]. The octahedral framework around Eu + can be related by a twinning operation (glide reflection) to the structure of ramsdellite (hep). 

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