Imagine a perfectly innocent quartz crystal that has grown to considerable size. It is lying there, at the bottom of a shallow sea, when a meterorite rudely invites itself to crash into the Earth’s surface with considerable noise, pressure, heat.
There is so much pressure and heat, in fact, that only a meteorite or asteroid can cause what happens next: the quartz is shocked!
Shocked quartz is quartz that has been subjected to an event that cannot happen from normal Earthly causes and which has had its very planar structure changed. The only two known causes of shocked quartz are nuclear explosions such as the Alamo field and the incredible impact forces of meteorites or ancient asteroids. The Pleistocene/Holcene astroid impact is one of the biggest culprits. This impact occured in North America about 12,000 years ago, creating a type of brecciated rock called impact breccia.
One aspect of the impact that creates shocked quartz, however, is that high heat is not involved, or the quartz would revert to its original structure. In some shocked quartz samples, the quartz resumed its normal growth pattern within a section of planar deformities.
Brecciated rock is like gravel that is cemented together in a finely grained matrix that may or may not have the same composition as the gravel. Impact breccia is formed through extra terrestial or nuclear impact and is generally found in or around impact craters.
Quartz crystals are said to be the second most abundant substance in the Earth’s crust. They are composed of silicon-oxygen tetrahedra where one oxygen molecule is shared between each two tetrahedron. The crystals grow perpetually in a six sided prism that terminates in a six sided pyramid.
Shocked quartz crystals contained shocked lamellae, or small fractures that create lines in the quartz that go along the planes of the crystal. These planes can usually only be viewed under a microscope.
But often, special microscope techniques, such as electron microscope, high resolution transmission electron microscopy (TEM), Focused Ion Beam (FIB) tomography, cross polarization, reflected light, thin slicing and polishing are required before the microscopic deformations can be seen.
Sometimes, the deformations actually can be examined as if they were “pressure gauges”, with various deformities helping to identify the amount of pressure that it would have taken to create them. New methods of examining the samples are being used, with goals of gathering more information and images of smaller and younger samples.
The most famous sites for such impact craters include the Chicxulub structure on the Northern Yucatan Penninsula of Mexico, the Bavarian Town of NÖrdlingen, Arizona, India, and generally in the K-3 boundary between Cretaceous and Tertiary rocks.
http://en.wikipedia.org/wiki/Quartz
http://en.wikipedia.org/wiki/Breccia
http://www.onderzoekinformatie.nl/en/oi/nod/onderzoek/OND1334620/
