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.

Classification	Brief 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).
Achondrites	Stones without chondrules. They are more like Earth's igneous rocks than are the Chondrites.
Aubrites	Stones without chondrules. They are more like Earth's igneous rocks than are the Chondrites.
Diogenites	Differentiated igneous, calcium-poor
Eucrites	A basaltic meteorite, it is a differentiated igneous, silicate- and calcium-rich with pigeonite as the primary mafic mineral.
Howardites	A basaltic meteorite, it is a differentiated igneous, silicate- and calcium-rich with pigeonite as the primary mafic mineral.
Urelites	Differentiated igneous, silicate-rich and calcium-poor with olivine as the primary mafic mineral.
Chondrites	Stones with chondrules, they are rich in plagioclase, pyroxene and olivine.
Enstatite Chondrites	Group-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 EL	Has less metal and more oxidized iron than Type EH.
Type EH	Has more metal than Type EL.
Ordinary Chondrites	Stones 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 H3	Has many well defined chondrules.
Type H4	Slightly fewer well defined chondrules than H3.
Type H5	Fewer, less-well defined chondrules than H4.
Type H6	Chondrules are few and poorly defined.
Olivine-hypersthene	Group-L, contains olivine and hypersthene and a free metal content of 7-12%. Richer in oxygen than Group-H.
Type L3	Has many well defined chondrules.
Type L4	Slightly fewer well defined chondrules than L3.
Type L5	Fewer, less-well defined chondrules than L4.
Type L6	Chondrules are few and poorly defined.
Amphoterites	Group-LL, these are iron- and metal-poor. Richer in oxygen than Group-L.
Type LL3	Has many well defined chondrules.
Type LL4	Slightly fewer well defined chondrules than LL3.
Type LL5	Fewer, less-well defined chondrules than LL4.
Type LL6	Chondrules 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 CI1	Volatile rich with water-bearing minerals, these are without chondrules and are quite rare.
Type CM2	Volatile rich with with sharply defined minichondrules and less than 20% nickel with very little, if any, taenite present.
Type CO3	Volatile rich with sharply defined minichondrules. Kamacite and taenite are present and the nickel content can exceed 20%.
Type CV3	Refractory rich with with sharply defined chondrules. The Allende meteorite is in this group.
Type C4	Has well-defined chondrules. Kamacite and taenite are present and the nickel content can exceed 20%.
Type C5	Water-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.
Lodranites	Composed of equal amounts of nickel-iron, olivine and pyroxene.
Mesosiderites	Composed equally of nickel-iron and silicates, primarily hypersthene and plagioclase.
Pallasites	Consists 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.
IAB	Chemistry-based group.
IC	Chemistry-based group.
IIAB	Chemistry-based group.
IIC	Chemistry-based group.
IID	Chemistry-based group.
IIE	Chemistry-based group.
IIF	Chemistry-based group.
IIIAB	Chemistry-based group.
IIICD	Chemistry-based group.
IIIE	Chemistry-based group.
IIIF	Chemistry-based group.
IVA	Chemistry-based group.
IVB	Chemistry-based group.
Ataxites	Structural Group-D, they are more than 16% nickel.
Octahedrites	Structural Group-O, they are between 7% and 12% nickel. This group is subdivided based on the band-width of their kamacite lamellae.
Group Ogg	Have the coarsest kamacite lamellae size at > 3.3mm.
Group Og	Coarse kamacite lamellae sized at 1.3mm to 3.3mm.
Group Om	Medium kamacite lamellae sized at 0.5 to 1.3mm.
Group Of	Fine kamacite lamellae sized at 0.2 to 0.5mm.
Group Off	Finest kamacite lamellae sized at less than 0.2mm.
Group Opl	Plessitic sized at less than 0.2mm.
Hexahedrites	Structural 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.