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| Cristobalite | |
|---|---|
 Cristobalite spherulites formed by devitrification from the obsidian matrix. Specimen from California, US; size: 5.9 cm × 3.8 cm × 3.8 cm (2.3 in × 1.5 in × 1.5 in). | |
| General | |
| Category | Oxide mineral, quartz group |
| Formula (repeating unit) | SiO2 |
| IMA symbol | Crs[1] |
| Strunz classification | 4.DA.15 |
| Dana classification | 75.1.1.1 |
| Crystal system | Tetragonal |
| Crystal class | Trapezohedral (422) |
| Space group | P41212, P43212 |
| Unit cell | a = 4.9709(1) Å, c = 6.9278(2) Å; Z = 4 (α polytype) |
| Structure | |
| Jmol (3D) | Interactive image |
| 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 (SMILES input only shows in Preview. SMILES is used to create the Jmol 3D image.) | |
| Identification | |
| Color | Colorless, white |
| Crystal habit | Octahedra or spherulites up to several cm in diameter |
| Twinning | on {111} |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 6–7 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent |
| Specific gravity | 2.32–2.36 |
| Optical properties | Uniaxial (−) |
| Refractive index | nω = 1.487 nε = 1.484 |
| Birefringence | 0.003 |
| Pleochroism | None |
| Melting point | 1,713 °C (3,115 °F) (β)[2] |
| References | [3][4][5][6] |
Cristobalite (/krɪˈstoʊbəˌlaɪt/) 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.
It is used in dentistry as a component of alginate impression materials as well as for making models of teeth.[7]
- ^ Warr, L. N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Deer, W. A.; Howie, R. A.; Zussman, J. (1966). An Introduction to the Rock Forming Minerals. Longman. pp. 340–355. ISBN 0-582-44210-9.
- ^ Mineralienatlas.
- ^ Cristobalite Archived 2010-07-15 at the Wayback Machine. Handbook of Mineralogy.
- ^ Cristobalite. Mindat.
- ^ "Cristobalite Mineral Data". Webmineral.
- ^ Anusavice, Kenneth J. (2013). Phillips' science of dental materials. Elsevier/Saunders. ISBN 978-1-4377-2418-9. OCLC 934359978.