Impactite
Impactite is rock created or modified by one or more impacts of a meteorite.<ref>Template:Cite journal</ref><ref name=":0">Template:Citation</ref> Impactites are considered metamorphic rock, because their source materials were modified by the heat and pressure of the impact.<ref name=":1">Template:Cite web</ref> On Earth, impactites consist primarily of modified terrestrial material, sometimes with pieces of the original meteorite.<ref name=":1" />
Formation
When a large meteorite hits a planet, it can radically deform the rocks and regolith that it hits. The heat, pressure, and shock of the impact changes these materials into impactite.<ref name=":1" /> Only very massive impacts generate the heat and pressure needed to transform a rock, so impactites are created rarely.<ref name=":1" />
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. Such material may contain preserved signs of ancient life—if life existed.<ref name="NASA-20150608">Template:Cite web</ref> Impactites are generally classified into three groups: shocked rocks, impact melt, and impact breccias.<ref name=":0" />
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.
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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.<ref name=":0" /> If the liquid solidifies quickly before the atoms arrange into a crystal lattice, it forms an impact glass. Impact glass can be dark brown, almost black, and partly transparent.<ref>Template:Cite web</ref> 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.<ref name=":0" />
Tektites
Template:Main Tektites are a rare kind of impact glass.<ref>Template:Citation</ref>
Impact breccias
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Breccia is "a rock consisting of angular fragments cemented together".<ref>Template:Cite book</ref> An impact breccia is formed when a meteor shatters a rock and then cements it back together. Some breccias contain impact melts.<ref name=":1" />
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<ref name="NASA-20150608" />
- Barringer crater, Arizona, United States<ref>Meteor Crater Bomblets</ref>
- Charlevoix impact structure, Québec, Canada
- Darwin Crater, Tasmania (source of Darwin glass)
- Lake Lappajärvi, Finland (source of Kärnäite)
- Manicouagan impact structure, Québec, Canada
- Neugrund crater, Estonia
- Nördlinger Ries crater, Germany
- Rochechouart impact structure, France
- Stac Fada Member, Scotland
- Wabar craters, Saudi Arabia
See also
References
External links
Template:Impact cratering on Earth Template:MeteoritesTemplate:Glass production techniques Template:Authority control