Cristobalite
The cristobalite is the cubic phase of high temperature of the Silice. The same type of layer that exists in the Tridymite is present also in cristobalite, but the topology of the connections between successive layers is different: the tetrahedrons are here in configuration trans instead of cis and consequently the continuous channels which exist in tridymite are replaced in cristobalite by cages.
The transition cristobalite → tridymite is reconstructive and cristobalite can thus remain in a metastable area. At low temperature it gives a polymorphic tétragonal (α), entirely metastable phase.
Cristobalite is formed at high temperature in the acid rocks igneous, but can be also formed at lower temperature in biochemical deposits.
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