Crystal structure model with oxygen polyhedra surrounding a cat ion in the centre. Yellow oxygen tetrahedra: containing lithium (Li), blue tetrahedra with beryllium (Be), red tetrahedra with silicon (Si), green octahedra with aluminium (Al), and red spheres indicating caesium (Cs) positions. Solid outlines mark the superstructure cell. Substitutions in tetrahedral and octahedral positions by other elements such as Ti, Ca, Mn, Fe, Na, K, Rb and Sc see Laurs et al. (2003) and Box 4B.

Rotating the crystal model of pezzottaite (P6a-c) shows the arrangement of caesium (Cs) in the direction of the c-axis within the channels. The Cs atoms are surrounded by six-membered rings involving Si, and 2 different types of twelve-membered rings. One ring is composed of Be and Al and the second composed of Be, Al and Li. With further rotation of the unit-cell, the complexity of the pezzottaite crystal structure becomes more clearly visible and the third dimension of the complicated crystal structure is more exposed (Fig. P6b). In a view perpendicular to the c-axis (Fig. P6c), the arrangement of Cs in the channels in the direction of the c-axis become visible. In the case of beryl, channels may be partially occupied by H2O, while in pezzottaite, the corresponding position is mainly occupied by Cs.