At what pressure does quartz transform into stishovite?

In the study of high-pressure phenomena, quartz (SiO${}_2$) undergoes a structural phase transition to the denser mineral stishovite at approximately 8 GPa.1

This transformation is a result of structural rearrangement, where the silicon atoms, which are four-coordinated in quartz, shift to a six-coordinated octahedral arrangement with oxygen atoms. Because stishovite is a high-pressure polymorph, it is typically found in nature only in environments subjected to extreme, sudden pressure, such as meteorite craters, or within deep-seated Earth formations like the upper mantle.123