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Stishovite
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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.
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Encyclopedia
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).
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