cristobalite

{{Infobox mineral | name = Cristobalite | category = Tectosilicate minerals | group = Quartz group | boxwidth = | boxbgcolor = | image = Cristobalite-Fayalite-40048.jpg | caption = Cristobalite spherulites formed by devitrification from the obsidian matrix. | formula = | IMAsymbol=Crs | molweight = | strunz = 4.DA.15 | dana = 75.1.1.1 | system = Tetragonal | class = Trapezohedral (422) | symmetry = P41212, P43212 | unit cell = a = 4.9709(1) Å, c = 6.9278(2) Å; Z = 4 (α polytype) | color = Colorless, white | habit = Octahedra or spherulites up to several cm in diameter | twinning = on {111} | cleavage = | fracture = Conchoidal | tenacity = Brittle | mohs = 6–7 | luster = Vitreous | refractive = nω = 1.487 nε = 1.484 | opticalprop = Uniaxial (−) | birefringence = 0.003 | pleochroism = None | streak = White | gravity = 2.32–2.36 | density = | melt = (β) | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent | other = | references = | SMILES = O[Si]3(O)O[Si](O)(O[Si]4(O)O)O[Si](O)(O)O[Si](O0)(O)O[Si]1(O)O[Si]5(O3)O[Si]2(O)O[Si](O4)(O)O[Si]0(O)O[Si](O)(O)O[Si](O)(O[Si](O)(O)O1)O[Si](O)(O2)O[Si](O)(O)O[Si](O)(O)O[Si](O)(O)O5 | Jmol = O[Si]3(O)O[Si](O)(O[Si]4(O)O)O[Si](O)(O)O[Si](O0)(O)O[Si]1(O)O[Si]5(O3)O[Si]2(O)O[Si](O4)(O)O[Si]0(O)O[Si](O)(O)O[Si](O)(O[Si]6(O)O1)O[Si](O)(O2)O[Si](O)(O)O[Si](O)(O[Si](O)(O)O6)O[Si](O)(O)O5 }}

Cristobalite ( ) is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the quartz group, which also include coesite, tridymite and stishovite. It is named after Cerro San Cristóbal in Pachuca Municipality, Hidalgo, Mexico.