Silicate and zeolite structures

Zeolites are formed by corner-sharing [SiO₄]^4- and [AlO₄]^5- tetrahedra with exchangeable cations keeping overall electrical neutrality. The tetrahedra are able to link using up to all 4 corners, thus forming a wide variety of different structures.

Linked tetrahedral are normally represented by drawing a straight line to represent the oxygen bridges connecting tetrahedra (fig. 20). This framework representation gives a clear view of the shapes of the cages and channels in the zeolite.

Many zeolite structures are based on a building unit consisting of 24 silica or alumina tetrhedra linked together in 4- and 6-rings forming a truncated octahedron. This is a sodalite unit (fig. 20).