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The Meteorite Classification System

The system of classification used for meteorites is a dynamic one. As new discoveries are made, the system is updated to accomodate the new members of the meteorite family. Note that not all meteorites fit into the categories listed below. These are anomalous meteorites that are to few in number to justify the creation of a new meteorite group.

There are three main classes of meteorites: Stoney (Aerolites), Stoney-Iron (Siderolites) and Iron (Siderites).

In the table below, each subgroup of a higher level group is indented. Meteorites in a group have one or more properties in common. Please note that the descriptions given for each group are brief and not comprehensive.



ClassificationBrief Description
Aerolites (Stoney)Commonly referred to as Stones, they are mostly made up of silicate minerals. They are divided into two main groups: Chondrites (those having chondrules) and Achondrites (those lacking chondrules).
AchondritesStones without chondrules. They are more like Earth's igneous rocks than are the Chondrites.
AubritesStones without chondrules. They are more like Earth's igneous rocks than are the Chondrites.
DiogenitesDifferentiated igneous, calcium-poor
EucritesA basaltic meteorite, it is a differentiated igneous, silicate- and calcium-rich with pigeonite as the primary mafic mineral.
HowarditesA basaltic meteorite, it is a differentiated igneous, silicate- and calcium-rich with pigeonite as the primary mafic mineral.
UrelitesDifferentiated igneous, silicate-rich and calcium-poor with olivine as the primary mafic mineral.
ChondritesStones with chondrules, they are rich in plagioclase, pyroxene and olivine.
Enstatite ChondritesGroup-E, the main silicate is enstatite and is 13-25% low-nickel-content metal. Sub-groups are defined based on their iron content and petrologic grade.
Type ELHas less metal and more oxidized iron than Type EH.
Type EHHas more metal than Type EL.
Ordinary ChondritesStones with chondrules and aggregates of silicate minerals which.
Olivine-bronzite Group-H, has equal proportions of olivine and bronzite and the greatest amount of iron. These have a free metal content of 16-21% with a nickel content of 7-12%.
Type H3Has many well defined chondrules.
Type H4Slightly fewer well defined chondrules than H3.
Type H5Fewer, less-well defined chondrules than H4.
Type H6Chondrules are few and poorly defined.
Olivine-hyperstheneGroup-L, contains olivine and hypersthene and a free metal content of 7-12%. Richer in oxygen than Group-H.
Type L3Has many well defined chondrules.
Type L4Slightly fewer well defined chondrules than L3.
Type L5Fewer, less-well defined chondrules than L4.
Type L6Chondrules are few and poorly defined.
AmphoteritesGroup-LL, these are iron- and metal-poor. Richer in oxygen than Group-L.
Type LL3Has many well defined chondrules.
Type LL4Slightly fewer well defined chondrules than LL3.
Type LL5Fewer, less-well defined chondrules than LL4.
Type LL6Chondrules are few and poorly defined.
Carbonaceous
Chondrite
Group-C, these contain organic compounds, volatile elements and very little or no free metal. These are thought to be the most primitive of all meteorites.
Type CI1Volatile rich with water-bearing minerals, these are without chondrules and are quite rare.
Type CM2Volatile rich with with sharply defined minichondrules and less than 20% nickel with very little, if any, taenite present.
Type CO3Volatile rich with sharply defined minichondrules. Kamacite and taenite are present and the nickel content can exceed 20%.
Type CV3Refractory rich with with sharply defined chondrules. The Allende meteorite is in this group.
Type C4Has well-defined chondrules. Kamacite and taenite are present and the nickel content can exceed 20%.
Type C5Water-poor relative to the other Carbonaceous Chondrites with chondrules that are not as well defined.
Siderolites (Stoney-Iron)Commonly referred to as Stoney-Irons since they are approximately 50% nickel-iron and 50% silicate minerals.
LodranitesComposed of equal amounts of nickel-iron, olivine and pyroxene.
MesosideritesComposed equally of nickel-iron and silicates, primarily hypersthene and plagioclase.
PallasitesConsists of a matrix of nickel-iron with embedded grains of olivine. It is a differentiated silicate-rich meteorite.
Siderites (Iron)Commonly referred to as Irons. There are 13 groups based on chemistry and 3 groups based on structure. The 13 chemistry-based groups are determined based on the amount of nickel, gallium, germanium and iridium present in the meteorite.
IABChemistry-based group.
ICChemistry-based group.
IIABChemistry-based group.
IICChemistry-based group.
IIDChemistry-based group.
IIEChemistry-based group.
IIFChemistry-based group.
IIIABChemistry-based group.
IIICDChemistry-based group.
IIIEChemistry-based group.
IIIFChemistry-based group.
IVAChemistry-based group.
IVBChemistry-based group.
AtaxitesStructural Group-D, they are more than 16% nickel.
OctahedritesStructural Group-O, they are between 7% and 12% nickel. This group is subdivided based on the band-width of their kamacite lamellae.
Group OggHave the coarsest kamacite lamellae size at > 3.3mm.
Group OgCoarse kamacite lamellae sized at 1.3mm to 3.3mm.
Group OmMedium kamacite lamellae sized at 0.5 to 1.3mm.
Group OfFine kamacite lamellae sized at 0.2 to 0.5mm.
Group OffFinest kamacite lamellae sized at less than 0.2mm.
Group OplPlessitic sized at less than 0.2mm.
HexahedritesStructural Group-H, they are 5% to 6% nickel and have crystals of kamacite.

This Meteorite Classification System document was conceived and prepared by Jim Plaxco.


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