- Shocked quartz
Shocked quartz is a form of
quartz that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the crystalline structure of quartz will be deformed along planes inside the crystal. These planes, which show up as lines under a microscope, are calledplanar deformation features (PDFs), or shock lamellae.Discovery
Shocked quartz was discovered after underground nuclear bomb testing, which caused the intense pressures required to form shocked quartz.
Eugene Shoemaker showed that shocked quartz is also found inside craters created by meteor impact, such as theBarringer Crater . [cite paper|author=Eugene M. Shoemaker|title=Impact mechanics at Meteor crater, Arizona|publisher=U.S. Atomic Energy Commission Open File Report|date=1959] The presence of shocked quartz proves that these craters were formed by an impact: avolcano would not generate the pressure required.Prevalence
Shocked quartz is found worldwide, in a thin
K-T Boundary at the boundary betweenCretaceous andTertiary rocks. This is further evidence (in addition toiridium enrichment) that the transition between the two geological eras was caused by a large impact.tructure
Shocked quartz is associated with two high pressure polymorphs of
silicon dioxide :coesite andstishovite . These polymorphs have a different crystal structure than standard quartz. Again, this structure can only be formed by intense pressure, but moderate temperatures. High temperatures would anneal the quartz back to its standard form. Coesite and stishovite are also indicative of impact (ornuclear explosion ).References
ee also
*
Breccia
*Lechatelierite
*Shatter cone External links
* [http://www.scn.org/~bh162/shocked_quartz.html Shocked quartz page]
* [http://mineral.galleries.com/minerals/silicate/coesite/coesite.htm Coesite page]
* [http://mineral.galleries.com/minerals/oxides/stishovi/stishovi.htm Stishovite page]
Wikimedia Foundation. 2010.