View source for Meteorite classification

{{short description|Systems of grouping meteorites based on shared characteristics}}
{{Use dmy dates|date=March 2014}}

In [[meteoritics]], a '''meteorite classification''' system attempts to group similar [[meteorite|meteorites]] and allows scientists to communicate with a standardized terminology when discussing them. Meteorites are classified according to a variety of characteristics, especially [[mineralogy|mineralogical]], [[petrology|petrological]], [[chemistry|chemical]], and [[isotope|isotopic]] properties.
[[File:Meteorites.jpg|thumb|Meteorites]]

==Terminology==
There is no single, standardized terminology used in meteorite classification; however, commonly used terms for categories include ''types'', ''classes'', ''clans'', ''groups'', and ''subgroups''. Some researchers hierarchize these terms, but there is no consensus as to which hierarchy is most appropriate. Meteorites that do not fit any known group (though they may fit somewhere within a higher level of classification) are ''ungrouped''.

==Genetic relationships==
Meteorite classification may indicate that a "genetic" relationship exists between similar meteorite specimens. Similarly classified meteorites may share a common origin, and therefore may come from the same [[astronomical object]] (such as a [[planet]], [[asteroid]], or [[natural satellite|moon]]) known as a ''parent body''. However, with current scientific knowledge, these types of relationships between meteorites are difficult to prove.

==Traditional classification scheme==
Meteorites are often divided into three overall categories based on whether they are dominantly composed of rocky material ([[stony meteorite]]s), metallic material ([[iron meteorite]]s), or mixtures ([[stony–iron meteorite]]s).  These categories have been in use since at least the early 19th century but do not have much genetic significance; they are simply a traditional and convenient way of grouping specimens.  In fact, the term "stony iron" is a misnomer as currently used. One group of chondrites (CB) has over 50% metal by volume and contains meteorites that were called stony irons until their affinities with chondrites were recognized.  Some iron meteorites also contain many [[silicate]] [[Inclusion (mineral)|inclusions]] but are rarely described as stony irons.

Nevertheless, these three categories sit at the top of the most widely used meteorite classification system. Stony meteorites are then traditionally divided into two other categories: chondrites (groups of meteorites that have undergone little change since their parent bodies originally formed and are characterized by the presence of [[chondrule]]s), and [[achondrite]]s (groups of meteorites that have a complex origin involving asteroidal or [[planetary differentiation]]).  The iron meteorites were traditionally divided into objects with similar internal structures ([[octahedrite]]s, [[hexahedrite]]s, and [[ataxite]]s), but these terms are now used for purely descriptive purposes and have given way to modern chemical groups.  Stony–iron meteorites have always been divided into [[pallasite]]s (which are now known to comprise several distinct groups) and [[mesosiderite]]s (a textural term that is also synonymous with the name of a modern group).

Below is a representation of how the meteorite groups fit into the more traditional classification hierarchy:<ref name="Weisberg 2006" /> 

{{hidden begin|border=5px  #aca solid|title=Stony meteorites|ta1=left}}
{{Tree list}}
* '''[[Chondrite]]s'''
** [[Carbonaceous chondrite]] class
*** [[CI chondrite]]s (Ivuna-like) group
*** CM-CO chondrite (mini-chondrule) clan
**** CM chondrite (Mighei-like) group
**** CO chondrite (Ornans-like) group
*** CV-CK chondrite clan
**** CV chondrite (Vigarano-like) group
***** CV-oxA chondrite (oxidized, [[Allende Meteorite|Allende]]-like) subgroup
***** CV-oxB chondrite (oxidized, Bali-like) subgroup
***** CV-red chondrite (reduced) subgroup
**** CK chondrite (Karoonda-like) group
*** CR chondrite clan
**** CR chondrite (Renazzo-like) group
**** CH chondrite (Allan Hills 85085-like) group
**** CB chondrite (Bencubbin-like) group
***** CBa chondrite subgroup
***** CBb chondrite subgroup
** [[Ordinary chondrite]] class
*** [[H chondrite]] group
*** [[L chondrite]] group
*** [[LL chondrite]] group
** [[Enstatite chondrite]] class
*** EH chondrite group
*** EL chondrite group
**Other chondrite groups, not in one of the major classes
*** R chondrite (Rumuruti-like) group
*** K chondrite (Kakangari-like) grouplet (a grouplet is a provisional group with <5 members)
* '''[[Achondrite]]s'''
** Primitive achondrites
*** Acapulcoite group
*** Lodranite group
*** Winonaite group
** Asteroidal achondrites
*** [[HED meteorite]] clan (possibly from asteroid [[4 Vesta]], also called basaltic achondrites)
**** [[Howardite]] group
**** [[Eucrite]] group
**** [[Diogenite]] group
*** [[Angrite]] group
*** [[Aubrite]] group (enstatite achondrites)
*** [[Ureilite]] group
*** Brachinite group
** [[Lunar meteorite]] group
** [[Martian meteorite]] group (sometimes called "SNC meteorites")
*** [[Shergottites]]
*** [[Nakhlites]]
*** [[Chassignite]]s
*** Other Martian meteorites, e.g., [[ALH84001]]
{{Tree list/end}}
{{Hidden end}}

{{hidden begin|border=5px  #aad solid|title=[[Stony-iron meteorite]]s|ta1=left}}
{{Tree list}}
* '''[[Pallasite]]s'''
** Main group pallasites
** Eagle station pallasite grouplet
** Pyroxene pallasite grouplet
* '''[[Mesosiderite]] group'''
{{Tree list/end}}
{{Hidden end}}

{{hidden begin|border=5px  #daa solid|title=[[Iron meteorite]]s|ta1=left}}
{{Tree list}}
* '''Magmatic iron meteorite groups'''
** IC iron meteorite group
** IIAB iron meteorite group
** IIC iron meteorite group
** IID iron meteorite group
** IIF iron meteorite group
** IIG iron meteorite group
** IIIAB iron meteorite group
** IIIE iron meteorite group
** IIIF iron meteorite group
** IVA iron meteorite group
** [[IVB meteorites|IVB]] iron meteorite group
* '''"Non-magmatic" or primitive iron meteorite groups'''
** [[IAB meteorites|IAB]] iron meteorite "complex" or clan (formerly groups [[IAB meteorites|IAB]] and IIICD)<ref>{{cite journal |last1=Wasson |first1=J. T. |last2=Kallemeyn |first2=G. W. |date=July 2002 |title=The IAB iron-meteorite complex: A group, five subgroups, numerous grouplets, closely related, mainly formed by crystal segregation in rapidly cooling melts |journal=Geochimica et Cosmochimica Acta |volume=66 |issue=13 |pages=2445–2473 |doi=10.1016/S0016-7037(02)00848-7 |bibcode=2002GeCoA..66.2445W|hdl=2060/20020080608 |hdl-access=free }}</ref>
*** [[IAB meteorites|IAB]] main group
*** Udei Station grouplet
*** Pitts grouplet
*** sLL (low Au, Low Ni) subgroup
*** sLM (low Au, Medium Ni) subgroup
*** sLH (low Au, high Ni) subgroup
*** sHL (high Au, Low Ni) subgroup
*** sHH (high Au, high Ni) subgroup
** [[IIE iron meteorite]] group
{{Tree list/end}}
{{Hidden end}}

===Rubin classification===
A. E. Rubin (2000) classification scheme:

{{Meteorite_Catalog_Rubin_2000}}

===Alternative schemes===
[[File:Meteorite Classification after Weissberg McCoy Krot 2006 Stony Iron.svg|thumbnail|right|Meteorite classification after Weisberg, McCoy and Krot 2006.<ref name="Weisberg 2006">{{cite book |editor-first=Dante S. |editor-last=Lauretta |editor2-first=Harold Y. Jr.|editor2-last=McSween |others=Foreword by Richard P. Binzel |title=Meteorites and the early solar system II |date=2006 |publisher=[[University of Arizona Press]] |location=Tucson |isbn=978-0816525621 |chapter-url=http://haroldconnolly.com/EES%20716%20Fall%2009%20Reading/Lecture%201/Background%20reading/Weisberg_etal_MESSII.pdf |author=Michael K. Weisberg |author2=Timothy J. McCoy |author3=Alexander N. Krot |access-date=15 December 2012 |pages=19–52 |chapter=Systematics and Evaluation of Meteorite Classification |archive-date=22 March 2020 |archive-url=https://web.archive.org/web/20200322162045/http://haroldconnolly.com/EES%20716%20Fall%2009%20Reading/Lecture%201/Background%20reading/Weisberg_etal_MESSII.pdf |url-status=dead }}</ref>]]

Two alternative general classification schemes were recently published, illustrating the lack of consensus on how to classify meteorites beyond the level of groups. In the Krot et al. scheme (2003)<ref>{{cite book |last1=Krot |first1=A.N. |first2=K.|last2=Keil |first3=E.R.D. |last3=Scott |first4=C.A. |last4=Goodrich |first5=M.K. |last5=Weisberg |date=2003 |chapter=Classification of meteorites |title=Treatise on Geochemistry |volume=1 |pages=83–128 |publisher=[[Elsevier]]
|editor1-first=Heinrich D. |editor1-last=Holland |editor2-first=Karl K. |editor2-last=Turekian |doi=10.1016/B0-08-043751-6/01062-8 |isbn=978-0-08-043751-4 }}</ref> the following hierarchy is used:

* '''[[Chondrite]]s'''
* '''Nonchondrites'''
** Primitive
** Differentiated
*** [[Achondrite]]s
*** [[Stony iron]]s
*** [[Iron meteorite|Irons]]

In the Weisberg et al. (2006) scheme<ref>Weisberg et al. (2006) Systematics and Evaluation of Meteorite Classification. In, Meteorites and the Early Solar System II, 19-52 (D.S. Lauretta and H.Y. McSween, Eds.), Univ. Arizona press</ref> meteorites groups are arranged as follows:

* '''[[Chondrite]]s'''
* '''[[Primitive achondrites]]'''
* '''[[Achondrite]]s'''

where irons and stony–irons are considered to be achondrites or primitive achondrites, depending on the group.

==History==
Modern meteorite classification was worked out in the 1860s,<ref name="Weisberg 2006" /> based on [[Gustav Rose]]'s and [[Nevil Story Maskelyne]]'s classifications. Gustav Rose worked on the meteorite collection of the [[Museum für Naturkunde]], [[Berlin]] and Maskelyne on the collection of the [[British Museum]], [[London]].<ref name="Rose 1864">{{cite book|last=Rose|first=Gustav|title=Beschreibung und Eintheilung der Meteoriten auf Grund der Sammlung im mineralogischen Museum zu Berlin|date=1864|publisher=Königlichen Akademie der Wissenschaften: in Commission bei F. Dümmler's Verlags-Buchhandlung Harrwitz und Gossmann|location=Berlin|pages=161|language=de}}</ref><ref name="Maskelyne 1863?">{{cite book|last=Maskelyne|first=Nevil Story|title=Catalogue of the Collection of Meteorites exhibited in the Mineral Department of the British Museum|date=c. 1863|publisher=Woodfall & Kinder|location=London}}</ref> Rose was the first to make different categories for meteorites with chondrules (chondrites) and without (nonchondrites). Story-Maskelyne differentiated between siderites, siderolites and aerolites (now called [[iron meteorite]]s, [[stony-iron meteorite]]s and [[stony meteorite]], respectively).<ref name="Weisberg 2006" />

In 1872 [[Gustav Tschermak von Seysenegg|Gustav Tschermak]] published his first meteorite classification based on Gustav Rose's catalog from 1864:

{{Meteorite_Catalog_Tschermak_1872}}

In 1883 Tschermak modified Rose's classification again.<ref name="Tschermak 1883">{{cite journal|last=Tschermak|first=Gustav|title=Die Mikroskopische Beschaffenheit der Meteoriten erläutert durch photographische Abbildungen|journal=Smithsonian Contributions to Astrophysics|volume=4|pages=137|date=1883|publisher=E. Koch|location=Stuttgart|bibcode=1964SCoA....4..137T}}</ref>

Further modifications were made by [[Aristides Brezina]].<ref name="Weisberg 2006" />

The first chemical classification was published by [[Oliver C. Farrington]], 1907.<ref name="Farrington 1907">{{cite journal|last=Farrington|first=Oliver Cummings|title=Analysis of iron meteorites, compiled and classified|journal=Geologic Series|date=1907|volume=3|pages=59–110|url=https://archive.org/stream/analysesofironme35farr/analysesofironme35farr_djvu.txt|access-date=16 December 2012}}</ref>

[[George Thurland Prior]] further improved the classification based on mineralogical and chemical data,<ref name="Prior 1916">{{cite journal|last=Prior|first=George Thurland|title=On the genetic relationship and classification of meteorites|journal=Mineralogical Magazine|date=1916|volume=18|issue=83|pages=26–44|doi=10.1180/minmag.1916.018.83.04|bibcode=1916MinM...18...26P}}</ref><ref name="Prior 1920">{{cite journal|last=Prior|first=George Thurland|title=The classification of meteorites|journal=Mineralogical Magazine|date=1920|volume=19|issue=90|pages=51–63<!--|access-date=16 December 2012-->|doi=10.1180/minmag.1920.019.90.01|bibcode=1920MinM...19...51P}}</ref> introducing the terms [[mesosiderite]], [[lodranite]] and [[enstatite chondrite]].<ref name="Mason 1966">{{cite journal|last=Mason|first=Brian|title=The enstatite chondrites|journal=Geochimica et Cosmochimica Acta |date=1966 |volume=30 |issue=1|pages=23–39 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19750068368_1975068368.pdf |access-date=16 December 2012|bibcode = 1966GeCoA..30...23M |doi = 10.1016/0016-7037(66)90089-5 }}</ref> In 1923 he published a catalogue of the meteorites in the [[Natural History Museum, London|Natural History Museum]] ([[London]]). He describes his classification as based on Gustav Tschermak and Aristides Brezina with modifications by himself. His main subdivisions were:
# Meteoric Irons or Siderites
# Meteoric Stony-irons or Siderolites
# Meteoric Stones or Aerolites.
He subdivides the "Meteoric Stones" into those that have chondrules (Chondritic Meteoric Stones or Chondrites) and those that don't (Non-chondritic Meteoric Stones or Achondrites). The iron meteorites are subdivided according to their structures as [[ataxite]]s, [[hexahedrite]]s and [[octahedrite]]s.<ref name="Prior 1923" /> A complete overview of his classification is given in the box below:

{{Meteorite Catalog Prior 1923}}

[[Brian Harold Mason]] published a further revision in the 1960s.<ref name="Mason 1967">{{cite journal|last=Mason|first=Brian Harold|title=Meteorites|journal=American Scientist|date=1967|volume=55|issue=4|pages=429–455|jstor=27837038}}</ref>

==See also==
* [[Glossary of meteoritics]]
* [[Asteroid spectral types]]

== References ==
{{Reflist}}

==External links==
* [http://www.nhm.ac.uk/jdsml/research-curation/research/projects/metcat/metsPerGroup.dsml Meteorite frequencies by group] - National History Museum
* [http://www.nhm.ac.uk/jdsml/research-curation/research/projects/metcat/bgfamilytree.dsml Meteorite "family tree"] - National History Museum
* [http://class.meteorites.com.au/ Meteorite Classification List] - Meteorites Australia

{{Meteorites}}

[[Category:Meteorite subdivisions| ]]
[[Category:Classification systems]]

[[it:Meteorite#Classificazione]]