Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure, the crystalline structure of quartz is deformed along planes inside the crystal. These planes, which show up as lines under a microscope, are called planar deformation features (PDFs), or shock lamellae.
Photomicrograph of shocked quartz
Photomicrograph of a shocked quartz grain (0.13 mm across) from the Chesapeake Bay impact crater, showing shock lamellae
An impact crater is a depression in the surface of a solid astronomical body formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than the surrounding terrain. Impact craters are typically circular, though they can be elliptical in shape or even irregular due to events such as landslides. Impact craters range in size from microscopic craters seen on lunar rocks returned by the Apollo Program to simple bowl-shaped depressions and vast, complex, multi-ringed impact basins. Meteor Crater is a well-known example of a small impact crater on Earth.
500-kilometre-wide (310 mi) crater Engelier on Saturn's moon Iapetus
Recently formed (between July 2010 and May 2012) impact crater on Mars showing a pristine ray system of ejecta
50,000-year-old Meteor Crater east of Flagstaff, Arizona, U.S. on Earth
Eugene Shoemaker, pioneer impact crater researcher, here at a crystallographic microscope used to examine meteorites