Shocked quartz

Shocked quartz is a special form of the mineral quartz , which differs from the normal form due to its microscopic structure. Under enormous pressures (but relatively limited temperatures), as they occur in shock metamorphosis (or shock wave metamorphosis), the crystal structure of quartz is deformed at certain dislocation planes. These planes are visible under a polarizing microscope and are known as planar deformation lamellae (sometimes also shock lamellae ).

discovery

Shocked quartz from Suvasvesi

Shocked quartz was first encountered underground after nuclear weapon tests, which had provided the required high educational pressures. Eugene Shoemaker was then able to show that shocked quartz also occurs within meteorite craters that had been ejected by an impact. Examples are the Barringer Crater and the Chicxulub Crater . The presence of shocked quartz in these crater structures proves their impact nature. Such high pressures cannot be generated in volcanic explosions.

Occurrence

Shocked quartz occurs worldwide on impact craters and their ejecta, for example also in the thin Cretaceous-Tertiary boundary layer . In addition to the enrichment of iridium , the presence of shocked quartz is further evidence that the transition from Cretaceous rocks to those of the Tertiary ( Paleogene ) was interrupted by a huge impact. After Eugene Shoemaker was able to detect shocked quartz in the Barringer Crater, he also found shocked quartz in the city wall of Nördlingen .

association

Thin section with 0.13 millimeter large shocked quartz grains from the Chesapeake Bay crater , interspersed with planar deformation lamellae

Shocked quartz is associated with two high pressure modifications of silicon dioxide - coesite and stishovite . Compared to ordinary quartz, these two polymorphs have a very different crystal structure, which can only be established at extremely high pressures of over 2 gigapascals and at relatively moderate temperatures. However, if the very high temperatures continue unabated, Coesite and Stishovite would return to their original form. Both minerals are therefore also a further indication of an impact or a nuclear weapon explosion.

Web links

Commons : shocked quartz - collection of pictures, videos and audio files

Individual evidence

^ Eugene M. Shoemaker: Impact mechanics at Meteor crater, Arizona . In: US Atomic Energy Commission Open File Report . 1959.

[1] Eugene M. Shoemaker: Impact mechanics at Meteor crater, Arizona . In: US Atomic Energy Commission Open File Report . 1959.