Structures of silica
| alpha-quartz - granite, sandstone, rock crystal, amethyst. This is the most stable form of silica. It has a helical structure, and because the helix can be right- or left-handed, alpha quartz is optically active. | |
| beta quartz - closely related in structure to alpha quartz. Alpha quartz converts to beta quartz at 846K | |
| cristobalite This structure is related to the diamond structure. The Si atoms are arranged as the C atoms in diamond. O atoms bridge between pairs of adjacent Si atoms. | |
| sodalite This structure is made up of Si24O48 cages where the Si atoms are located on the vertices of a truncated octahedron. The sodalite cage is an important building block in zeolite structures. |