Impactites from Monturaqui Impact Crater

Impactite is rock created or modified by one or more impacts of a

meteorite A meteorite is a rock (geology), rock that originated in outer space and has fallen to the surface of a planet or Natural satellite, moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical ...

. 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 materials 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.

Formation

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 terrestria ...

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 (

suevite Suevite is a rock consisting partly of melted material, typically forming a breccia containing glass and crystal or lithic fragments, formed during an impact event. It forms part of a group of rock types and structures that are known as impact ...

s) and mixtures of the two, as well as sedimentary rocks with significant impact-derived components (shocked mineral grains,

tektites Tektites () are gravel-sized bodies composed of black, green, brown or grey natural glass formed from terrestrial debris ejected during meteorite impacts. The term was coined by Austrian geologist Franz Eduard Suess (1867–1941), son of Eduar ...

, 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. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

. 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 Shock metamorphism or impact metamorphism describes the effects of shock-wave related deformation and heating during impact events. The formation of similar features during explosive volcanism is generally discounted due to the lack of metamorp ...

caused by the impact. They include shatter cones and high-pressure minerals, for example

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 ...

Impact melts

When a meteor strikes a planet's surface, the energy released from the impact can melt rock and regolith into a liquid. When the liquid cools it forms a solid known as an impact melt. If the liquid solidifies quickly before the atoms arrange into a

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

, it forms an impact

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

. 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.

Tektites

Tektites are a rare kind of impact glass.

Impact breccias

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 ...

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

PIA19673-Mars-AlgaCrater-ImpactGlassDetected-MRO-20150608

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

* Barringer crater, 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 diame ...

, Tasmania (source of Darwin glass) * Lake Lappajärvi, Finland (source of Kärnäite) * Manicouagan impact structure, Québec, Canada * Neugrund crater, Estonia *

Nördlinger Ries The Nördlinger Ries is an impact crater and large circular depression in western Bavaria and eastern Baden-Württemberg. It is located north of the Danube in the district of Donau-Ries. The city of Nördlingen is located within the depression ...

crater, Germany *

Rochechouart impact structure Rochechouart impact structure or Rochechouart astrobleme is an impact structure in France. Erosion has over the millions of years mostly destroyed its impact crater, the initial surface expression of the asteroid impact, leaving highly deformed ...

, France * Stac Fada Member, Scotland *

Wabar craters The Wabar craters are impact craters located in Saudi Arabia first brought to the attention of Western scholars by British Arabist, explorer, writer and Colonial Office intelligence officer St John Philby, who discovered them while searching f ...

, Saudi Arabia

References

External links

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