Cristobalite is a low density of SiO2 homogenous much like variant, its thermodynamic stability region is 1470℃ ~ 1728 ℃ (pressure). Beta cristobalite for its high temperature phase, but it can be saved to the metastable form low temperature, until about 250 ℃ when the shift type phase change form alpha cristobalite. Although the cristobalite can be formed by SiO2 melt crystallization in the thermodynamic stability region, but most of the cristobalite nature are formed in the metastable conditions. Such as diatomaceous earth in the process of diagenetic transformation into quartzose flint or microcrystalline opal, opal, opal CT - C, their main mineral phases for alpha cristobalite).