Extinction [Shocked quartz]
Discussions by Yann Oliver
Up: Extinction [Proofs for an extraterrestrial impact]
During the collision of an asteroid on the earth, some microscopic flaws appear in quartz crystals, the so-called planar deformation features (PDF). They actually are thin rectilinear layers of amorphous silica. They are formed by pressures of a few gigapascals.
With time and metamorphism, water dissolves in the silica and finally forms microscopic bubbles.
Some other, mechanical rather than chemical, flaws also appear in the quartz rystals submitted to a few gigapascals: in some planes, one of the three crystal directions is symmetrical to the corresponding direction in the rest of the mineral.
These structures have been found in the K-T sediments.