Chemical group
A chemical group is a set of meteorites with closely matching chemistry, minerals and isotopes, believed to come from the same parent body.
Meteorite classification works at several levels. Broad classes such as chondrites or iron meteorites are divided into groups, sets of meteorites so similar in composition that they most likely share a single parent body. Examples include the H, L and LL ordinary chondrites, the CM and CV carbonaceous chondrites, the HED achondrites and iron groups such as IIIAB and IVA.
Groups matter because each represents a separate world. Counting groups and grouplets, and including ungrouped meteorites, suggests meteorite collections sample on the order of a hundred or more distinct parent bodies. By convention, a formal group needs at least five unpaired members. Smaller clusters of similar meteorites are called grouplets, and meteorites matching no existing group are listed as ungrouped.
The Cape York iron from Greenland belongs to group IIIAB, the largest iron group, and the howardite Kapoeta belongs to the HED group linked to the asteroid Vesta. Identifying a group cannot be done by eye. Researchers compare bulk chemistry, mineral compositions and oxygen isotopes for stones, and nickel, gallium, germanium and other trace elements for irons.
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