IIG meteorite
| IIG meteorites | |
|---|---|
| — Group — | |
| Type | Iron |
| Structural classification | Hexahedrite |
| Class | Magmatic |
| Subgroups |
|
| Parent body | IIG-IIAB |
| Composition | Meteoric iron (kamacite), nickel (4.1 to 4.9 %), much schreibersite (phosphorus), little sulfur |
| Total known specimens | 6 |
IIG meteorites are a group of iron meteorites. The group currently has six members. They are hexahedrites with large amounts of schreibersite. The meteoric iron is composed of kamacite.[1]
Naming and history
Iron meteorites are designated with a Roman numeral and one or two letters. Classification is based on diagrams in which nickel content of meteoric iron is plotted against trace elements. Clusters in these diagrams are assigned a row (Roman numeral) and a letter in alphabetical order. IIG meteorites are therefore from the second row, cluster G.[2]
The Bellsbank, La Primitiva and Tombigbee meteorites were iron meteorites that were found to have chemical and structural similarities in 1967.[3] Further descriptions were made in 1973 and in 1974 it was proposed that the three meteorites should be grouped into the "Bellsbank Trio" grouplet.[4][5] The group status, that requires five specimen was filled in 1984 by the Twannberg meteorite and in 2000 by the Guanaco meteorite.[6]
Description
IIG meteorites are hexahedrites. The meteoric iron has a low concentration of Nickel (4.1 to 4.9%) and is exclusively kamacite. IIGs contain large amounts of phosphorus in the form of schreibersite and very low concentrations of sulfur.[1][6]
Parent body
Trace elements of IIAB and IIG meteorites are offset, which was interpreted as the two groups forming on a separate planetesimal. Other explanations for the offset are melt inmiscibility. This process took place while the planetesimal was cooling off. First meteoric iron crystallized into a network of cavities and channels. Eventually crystallization cut off the channels and made cavities of trapped melt. When the remaining melt reached the eutectic point, the cavities crystallized a mixture of schreibersite and meteoric iron. The matrix of this process would form the IIAB meteorites, while the cavities would form the IIG meteorites.[1]
Specimen
The IIG group currently has 6 meteorites that are assigned to it. The Bellsbank, La Primitiva, Tombigbee, Twannberg, Guanaco and the Auburn meteorite.[7]
See also
References
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