Hardest oxide
- Who
- Unknown
- Where
- Not Applicable
- When
- 01 January 1961
Stishovite has a KH of 33 (equal to a Mohs hardness of 7.5–8), and is also the fourth hardest substance yet discovered. It is a high-pressure modification of SiO2 (quartz) and can be formed by asteroid and meteorite impacts. The presence of stishovite is strong geological evidence that an impact crater is nearby.
KH stands for Knoop Hardness and is defined as the impression made in the surface as a function of an imposed load.
Stishovite was first synthesised in 1961, before it was first discovered at Barringer Crater, Arizona, by Eugene Shoemaker and colleages.