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| Formula | SiO2 |
| | Optic class & sign | Uniaxial negative |
| | Relief | Moderate-negative |
| | Refractive indices | no = 1.487
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ne = 1.484
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| - |
| | Birefringence (max.) | 0.003 |
| | | - |
| | Sign of elongation | Length-slow, l (+); less common is length-fast, l (-) |
| | Interference figure | Impractical due to very low Δn and small crystal size |
| | Colour / pleochroism | Colourless |
| | Zoning | |
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| Form | Habit | Octahedra; cubes less common (both forms are pseudomorphs after cubic β-cristobalite); skeletal and dendritic forms; fibrous in spherulites, also intergrown with fibrous tridymite and sanidine |
| | | Surface | Euhedral to anhedral |
| | Cleavage | None; curved fractures |
| | Twinning | {111}, simple or multiple; lamellar {111} twinning may occur as a single set, or two sets of lamellae that intersect. |
| | Extinction | Symmetrical to {111} in sections parallel c, straight to cube faces; fibres normally show straight extinction to their long axis. |
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| Reaction textures | Pseudomorphic replacement by fine-grained quartz |
| | Alteration / decomposition | - |
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| Occurence | Ign | Silica-saturated lavas; cristobalite is best recognized as a precipitate in cavities and fractures; submicroscopic in the groundmass of volcanics; devitrification product. |
| | | Met | Siliceous xenoliths in high-temperature lavas; ultrahigh-temperature contact zones of such lavas forming buchites; pyrometamorphism of siliceous rocks caused by underground combustion of coal |
| | | Sed | |
| | | Hyd | Precipitate from hydrothermal alteration of volcanics |
| | | Other | Meteorites |
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| Distinctive properties | Habit, very low Δn, moderate-negative relief, occurrence |
| | Additional comments | Pseudocubic. Cubic β-cristobalite is the high-temperature stable form (at T >1470°C), but commonly inverted to α-cristobalite. α-cristobalite has no stability field. |
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