meteoritics Meteoritics is the science that deals with meteors, meteorites, and meteoroids. It is closely connected to cosmochemistry, mineralogy and geochemistry. A specialist who studies meteoritics is known as a ''meteoriticist''. Scientific research in ...

, a meteorite classification system attempts to group similar meteorites and allows scientists to communicate with a standardized terminology when discussing them. Meteorites are classified according to a variety of characteristics, especially

mineralogical Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the p ...

petrological Petrology () is the branch of geology that studies rocks and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly taught together ...

chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., w ...

, and isotopic properties.

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 A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

, asteroid, or

moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

) 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 meteorites), metallic material (

iron meteorite Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorite that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Most iron ...

s), or mixtures ( stony–iron meteorites). 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 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 A chondrule (from Ancient Greek χόνδρος ''chondros'', grain) is a round grain found in a chondrite. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids. Because chondrites repr ...

s), and

achondrite An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystalli ...

s (groups of meteorites that have a complex origin involving asteroidal or

planetary differentiation In planetary science, planetary differentiation is the process by which the chemical elements of a planetary body accumulate in different areas of that body, due to their physical or chemical behavior (e.g. density and chemical affinities). The p ...

). The iron meteorites were traditionally divided into objects with similar internal structures (

octahedrite Octahedrites are the most common structural class of iron meteorites. The structures occur because the meteoric iron has a certain nickel concentration that leads to the exsolution of kamacite out of taenite while cooling. Structure Octahedr ...

hexahedrite Hexahedrites are a structural class of iron meteorite. They are composed almost exclusively of the nickel–iron alloy kamacite and are lower in nickel content than the octahedrites. The nickel concentration in hexahedrites is always below 5.8% a ...

s, and ataxites), 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 pallasites (which are now known to comprise several distinct groups) and

mesosiderite Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic nickel-iron and silicate. They are breccias with an irregular texture; silicates and metal occur often in lumps or pebbles as well as in fine-grained ...

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: *

Chondrite A chondrite is a stony (non- metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form p ...

s ** Carbonaceous chondrite class *** CI chondrites (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-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 The ordinary chondrites (sometimes called the O chondrites) are a class of stony chondritic meteorites. They are by far the most numerous group, comprising 87% of all finds. Hence, they have been dubbed "ordinary". The ordinary chondrites are t ...

class ***

H chondrite The H type ordinary chondrites are the most common type of meteorite, accounting for approximately 40% of all those catalogued, 46% of the ordinary chondrites, and 44% of all chondrites. The ordinary chondrites are thought to have originated from ...

group ***

L chondrite The L type ordinary chondrites are the second most common group of meteorites, accounting for approximately 35% of all those catalogued, and 40% of the ordinary chondrites. The ordinary chondrites are thought to have originated from three parent a ...

group ***

LL chondrite The LL chondrites are a group of stony meteorites, the least abundant group of the ordinary chondrites, accounting for about 10–11% of observed ordinary-chondrite falls and 8–9% of all meteorite falls (see meteorite fall statistics). The ordi ...

group **

Enstatite chondrite Enstatite chondrites (E-type chondrites) are a rare form of meteorite, rich in the mineral enstatite. Only about 200 E-Type chondrites are currently known, comprising about 2% of the chondrites that fall on Earth.Norton, O.R. and Chitwood, L.A. F ...

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 An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystalli ...

s ** Primitive achondrites *** Acapulcoite group *** Lodranite group *** Winonaite group ** Asteroidal achondrites ***

HED meteorite HED meteorites are a clan (subgroup) of achondrite meteorites. HED stands for "howardite– eucrite–diogenite". These achondrites came from a differentiated parent body and experienced extensive igneous processing not much different from the mag ...

clan (possibly from asteroid

4 Vesta Vesta ( minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, t ...

, also called basaltic achondrites) ****

Howardite Howardites are achondritic stony meteorites that originate from the surface of the asteroid 4 Vesta, and as such are part of the HED meteorite clan. There are about 200 distinct members known. Characteristics They are a regolith breccia consisti ...

group **** Eucrite group ****

Diogenite Diogenites are a group of the HED meteorite clan, a type of achondritic stony meteorites. Origin and composition Diogenites are currently believed to originate from deep within the crust of the asteroid 4 Vesta, and as such are part of the HED m ...

group *** Angrite group ***

Aubrite Aubrites are a group of meteorites named for Aubres, a small achondrite meteorite that fell near Nyons, France, in 1836. They are primarily composed of the orthopyroxene enstatite and are often called enstatite achondrites. Their igneous origin ...

group (enstatite achondrites) ***

Ureilite Ureilite is a rare type of stony meteorite that has a unique mineralogical composition very different from that of other stony meteorites. This dark grey or brownish meteorite type is named after the village Novy Urey ( Cyrillic: ''Новый У ...

group *** Brachinite group ** Lunar meteorite group **

Martian meteorite A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, and traversed interplanetary space before landing on Earth as a meteorite. , 277 meteorites had been classified as Martian, less than half a percen ...

group (sometimes called "SNC meteorites") *** Shergottites ***

Nakhlites Nakhlites are a group of Martian meteorites, named after the first one, Nakhla meteorite. Nakhlites are igneous rocks that are rich in augite and were formed from basaltic magma about 1.3 billion years ago. They contain augite and olivine cry ...

***

Chassignite A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, and traversed interplanetary space before landing on Earth as a meteorite. , 277 meteorites had been classified as Martian, less than half a percen ...

s *** Other Martian meteorites, e.g.,

ALH84001 Allan Hills 84001 (ALH84001) is a fragment of a Martian meteorite that was found in the Allan Hills in Antarctica on December 27, 1984, by a team of American meteorite hunters from the ANSMET project. Like other members of the shergottite– nak ...

* Pallasites ** Main group pallasites ** Eagle station pallasite grouplet ** Pyroxene pallasite grouplet *

Mesosiderite Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic nickel-iron and silicate. They are breccias with an irregular texture; silicates and metal occur often in lumps or pebbles as well as in fine-grained ...

group * 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 iron meteorite group * "Non-magmatic" or primitive iron meteorite groups ** IAB iron meteorite "complex" or clan (formerly groups IAB and IIICD) *** 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 The iron meteorites of the IIE chemical type are octahedrites of various coarseness, most of which contain numerous inclusions of recrystallized stony silicates. Composition and origin They have mineral compositions and oxygen isotope ratios ver ...

group

Rubin classification

A. E. Rubin (2000) classification scheme:

Alternative schemes

Meteorite Classification after Weissberg McCoy Krot 2006 Stony Iron

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) the following hierarchy is used: *

s * Nonchondrites ** Primitive ** Differentiated ***

s *** Stony irons *** Irons In the Weisberg et al. (2006) schemeWeisberg 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 meteorites groups are arranged as follows: *

s * Primitive achondrites *

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, based on

Gustav Rose Prof Gustavus ("Gustav") Rose FRSFor HFRSE (18 March 1798 – 15 July 1873) was a German mineralogist who was a native of Berlin. He was President of the German Geological Society from 1863 to 1873. Life He was born in Berlin the son of pharmaco ...

's and

Nevil Story Maskelyne Mervyn Herbert Nevil Story Maskelyne (3 September 1823 – 20 May 1911) was an English geologist and politician. Scientific career Educated at Wadham College, Oxford, Maskelyne taught mineralogy and chemistry at Oxford from 1851, before becom ...

's classifications. Gustav Rose worked on the meteorite collection of the

Museum für Naturkunde The Natural History Museum (german: Museum für Naturkunde) is a natural history museum located in Berlin, Germany. It exhibits a vast range of specimens from various segments of natural history and in such domain it is one of three major muse ...

Berlin Berlin ( , ) is the capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's List of cities in the European Union by population within ci ...

and Maskelyne on the collection of the

British Museum The British Museum is a public museum dedicated to human history, art and culture located in the Bloomsbury area of London. Its permanent collection of eight million works is among the largest and most comprehensive in existence. It docum ...

London London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...

. 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

s, stony-iron meteorites and stony meteorite, respectively). In 1872 Gustav Tschermak published his first meteorite classification based on Gustav Rose's catalog from 1864: In 1883 Tschermak modified Rose's classification again. Further modifications were made by Aristides Brezina. The first chemical classification was published by Oliver C. Farrington, 1907. George Thurland Prior further improved the classification based on mineralogical and chemical data, introducing the terms

, lodranite and

enstatite chondrite Enstatite chondrites (E-type chondrites) are a rare form of meteorite, rich in the mineral enstatite. Only about 200 E-Type chondrites are currently known, comprising about 2% of the chondrites that fall on Earth.Norton, O.R. and Chitwood, L.A. F ...

. In 1923 he published a catalogue of the meteorites in the

Natural History Museum A natural history museum or museum of natural history is a scientific institution with natural history collections that include current and historical records of animals, plants, fungi, ecosystems, geology, paleontology, climatology, and more. ...

(

). 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 ataxites,

s and

s. A complete overview of his classification is given in the box below: Brian Harold Mason published a further revision in the 1960s.

References

External links

Meteorite frequencies by group
- National History Museum
Meteorite "family tree"
- National History Museum
Meteorite Classification List
- Meteorites Australia {{Meteorites it:Meteorite#Classificazione