b-Quartz

P6[2]22

Si is surrounded by 4 oxygen atoms. These tetrahedra are linked in a 3-D lattice.

The main difference between the low temperature version (a-quartz) and the high temperature version (b-quartz) is the symmetry. a-quartz is trigonal, whereas b-quartz is hexagonal. In both cases, the positions of atoms is about the same and the bonding is the same. When looking down the c-axis (the unit cell will appear as a diamond), the relatively large nearly circular hole is a 3-pointed star with 3 extra points in a-quartz, but is a 6-pointed star in b-quartz. This difference in symmetry is the result of minor twisting of the Si-tetrahedra.

Tridymite

P6/m 2/m 2/m

Crystobalite

F 4/m -3 2/m

Coesite

2/m