Impactite

{{Short description|Rock created or modified by impact of a meteorite}}

File:Impactites from Monturaqui Impact Crater.jpg impact crater, Chile)]]

Impactite is rock created or modified by one or more impacts of a meteorite.{{Cite journal|last1=Stöffler|first1=D.|last2=Grieve|first2=R.A.F.|title=Classification and Nomenclature of Impact Metamorphic Rocks: A Proposal to the IUGS Subcommission on the Systematics of Metamorphic Rocks |journal=Lunar and Planetary Science Conference| page = 1347|bibcode = 1994LPI....25.1347S|date=1994}}{{Citation|last1=Schmid|first1=Rolf|title=Classification and nomenclature scheme|work=Metamorphic Rocks|pages=3–110|publisher=Cambridge University Press|isbn=978-0-511-62891-7|last2=Fettes|first2=Douglas|last3=Harte|first3=Ben|last4=Davis|first4=Eleutheria|last5=Desmons|first5=Jacqueline|last6=Smulikowski|first6=Witold|last7=Sassi|first7=Francesco|last8=Brodie|first8=Kate|last9=Árkai|first9=Péter|editor2-first=Jacqueline|editor2-last=Desmons|editor1-first=Douglas|editor1-last=Fettes|year=2007|doi=10.1017/cbo9780511628917.003}} Impactites are considered metamorphic rock, because their source materials were modified by the heat and pressure of the impact.{{Cite web|title=Impactites: Impact Breccia, Tektites, Moldavites, Shattercones|url=https://geology.com/meteorites/impactites.shtml|access-date=2020-06-10|website=geology.com}} 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 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. Such material may contain preserved signs of ancient life—if life existed.{{cite web |author=Staff |title=PIA19673: Spectral Signals Indicating Impact Glass on Mars |url=http://photojournal.jpl.nasa.gov/catalog/PIA19673 |date=8 June 2015 |work=NASA |access-date=8 June 2015 }} 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.

File:Impactite (Pleistocene, ~816 ka; near Darwin Crater, Tasmania) 14.jpg

= 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, it forms an impact glass. Impact glass can be dark brown, almost black, and partly transparent.{{Cite web|last=Temming|first=Maria|title=Exotic Glass Could Help Unravel Mysteries of Mars|website=Scientific American|url=http://www.scientificamerican.com/article/exotic-glass-could-help-unravel-mysteries-of-mars/|access-date=2015-06-15}} 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.{{Citation |last=Koeberl |first=Christian |title=Tektites |date=2024-05-22 |work=Oxford Research Encyclopedia of Planetary Science |url=https://oxfordre.com/planetaryscience/display/10.1093/acrefore/9780190647926.001.0001/acrefore-9780190647926-e-263 |access-date=2025-05-11 |language=en |doi=10.1093/acrefore/9780190647926.013.263 |isbn=978-0-19-064792-6|url-access=subscription }}

= Impact breccias =

File:Impact breccia (Late Cretaceous, 70.3 Ma; Kara Impact Structure, Polar Urals, Russia).jpg

Breccia is "a rock consisting of angular fragments cemented together".{{Cite book |last=Holland |first=Stuart S. |url=http://cmscontent.nrs.gov.bc.ca/geoscience/PublicationCatalogue/Bulletin/BCGS_B048.pdf |title=Landforms of British Columbia: A Physiographic Outline |year=1976 |location=British Columbia, Canada |pages=127 |language=English}} An impact breccia is formed when a meteor shatters a rock and then cements it back together. Some breccias contain impact melts.