Coesite
Coesite (/ˈkoʊsaɪt/) is a form (polymorph) of silicon dioxide (SiO2) that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (700 °C, 1,300 °F), are applied to quartz. Coesite was first synthesized by Loring Coes, Jr., a chemist at the Norton Company, in 1953.
| Coesite | |
|---|---|
| General | |
| Category | Tectosilicate, quartz group |
| Formula (repeating unit) | SiO2 |
| IMA symbol | Coe |
| Strunz classification | 4.DA.35 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H–M symbol) |
| Space group | C2/c |
| Unit cell | a = 7.143 b = 12.383 c = 7.143 [Å] β = 120.00° Z = 16 |
| Identification | |
| Formula mass | 60.0843 g/mol |
| Color | Colorless |
| Crystal habit | Inclusions in UHP metamorphic minerals up to 3 mm in size |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 7.5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent |
| Density | 2.92 (calculated) |
| Optical properties | Biaxial |
| Refractive index | nx = 1.594 ny = 1.595 nz = 1.599 |
| Birefringence | +0.006 |
| 2V angle | 60–70 |
| References | |
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