Falling stars: All about shatter cones

When sleuthing a potential or known meteorite impact crater, scientists look for clues. One of these clues is a geological feature known as a “shatter cone.” These objects — also called shocked rocks — bear the patterns of high-energy impacts. They are found only in the bedrock under meteorite impact craters or near underground nuclear explosions. This gives us some idea of the power of a meteorite impact.
[caption image="http://cs.astronomy.com/asycs/cfs-filesystemfile.ashx/__key/CommunityServer.Blogs.Components.WeblogFiles/astronomy.Meteorites/8078.Sierra_2D00_Madera_2D00_shatter_2D00_cone_5F00_300.jpg" targeturl="http://cs.astronomy.com/asycs/cfs-filesystemfile.ashx/__key/CommunityServer.Blogs.Components.WeblogFiles/astronomy.Meteorites/8562.Sierra_2D00_Madera_2D00_shatter_2D00_cone.jpg"]This shatter cone comes from the Sierra Madera crater located in southwestern Pecos County, Texas. The crater is 8 miles (13 kilometers) in diameter. Estimates place its age at less than 100 million years. // All photos by Mike Reynolds[/caption]Shatter cones show that the rocks near the impact site have been subjected to a significant shock. The pressures associated with such impacts lie between 29,000 pounds per square inch to more than 4 million psi. Atmospheric pressure at sea level measures 14.7 psi, so such impactors create pressures some 270,000 times greater than our bodies normally experience.
Shatter cones are one type of impact evidence beyond the bowl-shaped crater. But the crater might have been erased from sight due to erosion, or it may be covered by growth. Impact “glasses,” ...