| Stishovite | |
|---|---|
| General | |
| Category | Mineral |
| Chemical formula | Silica (silicon dioxide, SiO2) |
| Identification | |
| Color | Clear (if no impurities); also see Varieties |
| Mohs scale hardness | 9.4 |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 4.28 when pure |
| Refractive index | nω = 1.81 |
| Melting point | 1650 (±75) °C |
| Solubility | 11.0 +/- 1.1 PPM @ 25 C |
Stishovite (after S.M. Stishov, 20th-century Russian mineralogist) is an extremely hard, dense tetragonal form (polymorph) of silicon dioxide. It was traditionally considered the hardest known oxide; however, boron suboxide was recently discovered to be much harder. At normal temperature and pressure, stishovite is metastable; it will eventually decay to quartz; however, this phase change is slow enough that it has never been observed. Stishovite was first discovered in nature and named by Edward C. T. Chao.
Synthesis[]
The only known occurrences of stishovite in nature formed at the very high shock pressures (>100 kbar = 10 GPa) and temperatures (> 1200°C) present during hypervelocity meteorite impact into quartz-bearing rock. Stishovite may also be synthesized by duplicating these conditions in the laboratory, either isostatically or through shock (see shocked quartz).
See also[]
- Coesite, a related mineral
References[]
High-pressure silica polymorphs as hardest known oxides
External links[]
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