Shocked quartz is a form of

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the

crystalline structure In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat ...

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.

Discovery

Shocked quartz was discovered following underground nuclear weapons testing, which generated the intense pressures required to alter the quartz lattice.

Eugene Shoemaker Eugene Merle Shoemaker (April 28, 1928 – July 18, 1997) was an American geologist. He co-discovered Comet Shoemaker–Levy 9 with his wife Carolyn S. Shoemaker and David H. Levy. This comet hit Jupiter in July 1994: the impact was telev ...

showed that shocked quartz is also found inside craters created by

meteor A meteor, known colloquially as a shooting star, is a glowing streak of a small body (usually meteoroid) going through Earth's atmosphere, after being heated to incandescence by collisions with air molecules in the upper atmosphere, creating a ...

impact, such as the Barringer Crater and

Chicxulub crater The Chicxulub crater is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore, but the crater is named after the onshore community of Chicxulub Pueblo (not the larger coastal town of Chicxulub Puerto). I ...

. The presence of shocked quartz supports that such craters were formed by impact, because a volcanic eruption would not generate the required pressure. Lightning is now known to contribute to the surface record of shocked quartz grains, complicating identification of hypervelocity impact features.

Formation

Shocked quartz is usually associated in nature with two high-pressure polymorphs of

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...

coesite Coesite () is a form (polymorphism (materials science), polymorph) of silicon dioxide (silicon, Sioxide, O2) that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (), are applied to quartz. Coesite was first ...

and

stishovite Stishovite is an extremely hard, dense tetragonal form ( polymorph) of silicon dioxide. It is very rare on the Earth's surface; however, it may be a predominant form of silicon dioxide in the Earth, especially in the lower mantle. Stishovite w ...

. These polymorphs have a crystal structure different from standard quartz. This structure can be formed only by intense pressure (more than 2 gigapascals), but at moderate temperatures. Coesite and stishovite are usually viewed as indicative of

impact event An impact event is a collision between astronomical objects causing measurable effects. Impact events have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal effe ...

s or eclogite facies metamorphism (or

nuclear explosion A nuclear explosion is an explosion that occurs as a result of the rapid release of energy from a high-speed nuclear reaction. The driving reaction may be nuclear fission or nuclear fusion or a multi-stage cascading combination of the two, th ...

), but are also found in sediments prone to

lightning Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...

strikes and in

fulgurite Fulgurites (), commonly called "fossilized lightning", are natural tubes, clumps, or masses of sintered, vitrified, or fused soil, sand, rock, organic debris and other sediments that sometimes form when lightning discharges into ground. Whe ...

Occurrence

Shocked quartz is found worldwide, and occurs in the thin

Cretaceous–Paleogene boundary The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end o ...

layer, which occurs at the contact between

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

and

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

rocks. This is further evidence (in addition to

iridium Iridium is a chemical element; it has the symbol Ir and atomic number 77. This very hard, brittle, silvery-white transition metal of the platinum group, is considered the second-densest naturally occurring metal (after osmium) with a density ...

enrichment) that the transition between the two geologic periods was caused by a large impact. Lightning also generates planar deformation features in quartz and is capable of propagating appropriate pressure/temperature gradients in rocks and sediments alike. This very common mechanism may significantly contribute to the accumulation of shocked quartz in the geologic record. Mantle xenoliths and sediments derived from them may contain coesite or stishovite. Though shocked quartz is only recently recognized,

discovered it prior to its crystallographic description in building stones in the

Bavaria Bavaria, officially the Free State of Bavaria, is a States of Germany, state in the southeast of Germany. With an area of , it is the list of German states by area, largest German state by land area, comprising approximately 1/5 of the total l ...

n town of Nördlingen, derived from shock-metamorphic rocks, such as

breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

and pseudotachylite, of

Ries crater Ries is the German word for a unit of paper ream, derived from the Arabic word ''rizma''. The term can refer to: Geography * Nördlinger Ries, a large circular depression in western Bavaria, Germany. * Ries (Graz), a district of the city of Gr ...

References

External links

Shocked quartz page

{{Impact cratering on Earth Quartz varieties Impact geology

Discovery

Formation

Occurrence

See also

References

External links