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Impactite is rock created or modified by one or more impacts of a
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...
. Impactites are considered
metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, caus ...
, because their
source material A source text is a text (sometimes oral) from which information or ideas are derived. In translation, a source text is the original text that is to be translated into another language. Description In historiography, distinctions are commo ...
s were modified by the heat and pressure of the impact. On Earth, impactites consist primarily of modified terrestrial material, sometimes with pieces of the original meteorite.


Creation

When a large meteorite hits a planet, it can radically deform the rocks and
regolith Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestr ...
that it hits. The heat, pressure, and shock of the impact changes these materials into impactite. Only very massive impacts generate the heat and pressure needed to transform a rock, so impactites are created rarely.


Characteristics

Impactite includes shock-metamorphosed target rocks, melts ( suevites) and mixtures of the two, as well as sedimentary rocks with significant impact-derived components (shocked mineral grains, tektites, anomalous geochemical signatures, etc.). In June 2015, NASA reported that impact glass has been detected on the planet
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
. Such material may contain preserved signs of ancient life—if life existed. Impactites are generally classified into three groups: shocked rocks, impact melt, and impact breccias.


Shocked rock

Shocked rocks have been transformed by shock metamorphism caused by the impact. They include shatter cones and high-pressure minerals, for example coesite 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 ...
.


Impact melts

When a meteor strikes a planet's surface, the energy released from the impact can melt rock and soil into a liquid. The liquid then cools and becomes an impact melt. If the liquid cools and hardens quickly into a solid, impact glass forms before the atoms have time to arrange into a
crystal lattice In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by : \mathbf = n_1 \mathbf_1 + n_2 \mathbf_2 + n ...
. Impact glass can be dark brown, almost black, and partly transparent. Sometimes, the cooled liquid does form a crystal structure. In that case, it would still be considered an impact melt, but not an impact glass.


Impact breccias

Breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...
is "a rock consisting of angular fragments cemented together". An impact breccia is formed when a meteor shatters a rock and then cements it back together. Some breccias contain impact melts.


Examples of impactite

Impactite has been found, for example, at the following impact craters and structures: * Alamo bolide impact (Late Devonian), Nevada, United States * Alga crater on the planet
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
*
Barringer crater Meteor Crater, or Barringer Crater, is a meteorite impact crater about east of Flagstaff and west of Winslow in the desert of northern Arizona, United States. The site had several earlier names, and fragments of the meteorite are offici ...
, Arizona, United StatesMeteor Crater Bomblets
/ref> * Charlevoix impact structure, Québec, Canada *
Darwin Crater Darwin Crater is a suspected meteorite impact crater in Western Tasmania about south of Queenstown, just within the Franklin-Gordon Wild Rivers National Park. The crater is expressed as a rimless circular flat-floored depression, in diam ...
, Tasmania (source of Darwin glass) * Lake Lappajärvi, Finland (source of Kärnäite) *
Manicouagan impact structure Manicouagan Reservoir (also Lake Manicouagan) is an annular lake in central Quebec, Canada, covering an area of . The lake island in its centre is known as René-Levasseur Island, and its highest point is Mount Babel. The structure was create ...
, Québec, Canada * Neugrund crater, Estonia * Nördlinger Ries crater, Germany *
Rochechouart impact structure Rochechouart impact structure or Rochechouart astrobleme is an impact structure in France. Erosion has over the millions of years has mostly destroyed its impact crater, the initial surface expression of the asteroid impact leaving highly deforme ...
, France *
Stac Fada Member The Stac Fada Member is a distinctive layer towards the top of the Mesoproterozoic Bay of Stoer Formation, part of the Stoer Group (lowermost Torridonian Supergroup) in northwest Scotland. This rock unit is generally thick and is made of sandsto ...
, Scotland * Wabar craters, Saudi Arabia


See also

*
Glossary of meteoritics This is a glossary of terms used in meteoritics, the science of meteorites. # * 2 Pallas – an asteroid from the asteroid belt and one of the likely parent bodies of the CR meteorites. * 4 Vesta – second-largest asteroid in the asteroid b ...
*
Meteorite shock stage Meteorite shock stage is a measure of the degree of fracturing of the matrix of a common chondrite meteorite. Impacts on the parent body of a meteoroid can produce very large pressures. These pressures heat, melt and deform the rocks. This is call ...
*
Vitrified sand Vitrified sand is sand that has been heated to a high enough temperature to undergo vitrification, which is the melting of the silicon dioxide or quartz that compose common sand. Vitrified sand is a type of natural glass, contrasted with manufactur ...


References


External links


Meteorite crater glossary
Metamorphic rocks Sedimentary rocks Meteorite mineralogy and petrology Impact event minerals Glass in nature {{Meteorite-stub