Alternative structural descriptions and symbols

All the requisite structural information for a solid phase is contained (either explicitly or implicitly) in the description of its unit cell. A number of features, however, which are especially relevant for chemical-physical considerations, such as local coordination geometries, the existence of clusters of atoms or chains or layers, etc., are not self-evident in the aforementioned structural descriptions and can be deduced only by means of a more or less complicated series of calculations. 

Another point which should be underlined is that the same structure can be differently viewed and described (Parthe and Gelato 1984, Franzen 1986). The simple rock-salt structure, for instance, can be viewed as a cubic close-packed set of anions with cations in octahedral holes, as XY6 octahedra sharing edges, as a stacking sequence of superimposed alternate triangular nets, respectively, of X and Y atoms 

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