Cristobalite, SiO

Fig. 4.4 Crystal structures of two more 1 2 compounds oxygen is the larger circle in both (a) unit cell of rutile, TiOj, tetragonal, space group P42/mnm (b) unit cell of -cristobalite, SiO,. [From Ladd, M. F. C. Structure and Bonding in Solid State Chemistry, Wiley ...

Cristobalite (SiO ) / tridymite (8102) derived, respectively, from a network of silicon atoms, zinc-blende, or wurtzite, with one atom of oxygen situated in the middle of each Si-Si segment BeF2 of cristobalite structure. 

If all the four corners of the SiO tetrahedra are shared, three-dimensional networks result. The different forms of silica (quartz, tridymite and cristobalite) discussed earlier in this section are typical examples. Feldspars are generated when part of the Si is... 

Cristobalite and tridymite are similarly made from SiO tetrahedra fused together by sharing oxygen atoms, with, ho vever, different arrangements of the tetrahedra in space than that of quartz. 

Silica, in its various forms, is a three-dimensional framework of SiO units which share all their corners. Cristobalite for instance has Si04 tetrahedra arranged as are the atoms in zinc blende tridymite as are those in wurtzite. 

Its existence at room temperature has been questioned by Geller and Thurmond (1955) who consider the X-ray diffraction pattern, formerly attributed to SiO, to arise from a mixture of P cristobalite and silicon carbide the carbon being derived from the reaction vessel. 

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