Stishovite

Dense, high-pressure phase of quartz; so far identified only in shock-metamorphosed, quartz-bearing rocks from meteorite impact craters. Stishovite was synthesized in 1961 before it was discovered at Meteor Crater, Arizona. Its structure consists of parallel chains of single SiO6 octahedra. The octahedra are on their sides, sharing opposing edges.
Stishovite structure
Image source: http://www.auburn.edu/~hameswe/Stishovitepage.html.

stishovite is believed to have formed only due to the high pressures generated by a meteorite impact. The discovery of stishovite in a K/T boundary clay has been used as convincing evidence of a meteorite impact at the time of the K/T boundary. http://www.science.smith.edu/geosciences/min_jb/SilicaPolymorphs.pdf