Editing Cristobalite (section)

=== Metastability ===
Cristobalite is stable only above 1470&nbsp;°C, but can crystallize and persist [[metastable|metastably]] at lower temperatures. The persistence of cristobalite outside its thermodynamic stability range occurs because the transition from cristobalite to [[quartz]] or [[tridymite]] is "reconstructive", requiring the breaking up and reforming of the [[silica]] framework. These frameworks are composed of SiO<sub>4</sub> [[tetrahedra]] in which every oxygen atom is shared with a neighbouring tetrahedron, so that the [[chemical formula]] of silica is SiO<sub>2</sub>. The breaking of these bonds, required to convert cristobalite to tridymite and quartz, requires considerable [[activation energy]] and may not happen on a human time frame at room temperature. Framework silicates are also known as [[Silicate minerals#Tectosilicates|tectosilicates]].

When [[Devitrification|devitrifying]] silica, cristobalite is usually the first phase to form, even when well outside its thermodynamic stability range. This is an example of [[Ostwald's rule|Ostwald's step rule]]. The dynamically disordered nature of the β phase is partly responsible for the low enthalpy of fusion of silica.