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Ungrouped Carbonaceous chondrites
Ungrouped Carbonaceous Chondrites
Some carbonaceous chondrites don't fit easily into the established groups, although they can be clearly identified as members of the class of carbonaceous chondrites. They are usually designated as CC ungrouped or CC UNGR and they probably represent other parent bodies of carbonaceous chondrites or source regions of the primordial solar nebula. Some of them are unique samples, while others show certain relations to each other and/or to established groups of carbonaceous chondrites.
Unique samples: A good example of an unique ungrouped carbonaceous chondrite is the witnessed meteorite fall of Tagish Lake, a rather primitive type 2 chondrite that initially has been thought to represent the first petrologic type 2 member of the CI group. However, subsequent studies have shown that it is unrelated to this primitive group of carbonaceous chondrites, and that it probably has his origin on another, so far unsampled parent body.
Groups and grouplets: Amoung classifying scientists it's an unwritten law in the naming of new meteorite groups that it needs at least five members to constitute a new group. However, certain new groups and grouplets have been proposed in the past, although they don't have the necessary number of established members. This is done to show obvious relations between these ungrouped meteorites, and these grouplets often are the precursors of new groups to be formed in the future.
The Coolidge grouplet, named for the meteorite of Coolidge that was found in Kansas, USA, in 1937, is a good example for such a "group in progress". Together with our own desert find, Sahara 00177, there are at least three other carbonaceous chondrites - officially designated as C UNGR - that show a similar high matrix to chondrule ratio as Coolidge as well as the same enrichment in refractory elements. Maybe this grouplet will gain the status of a fully accepted group as soon as new members are found and recognized in the wealth of new meteorite finds from the hot deserts of Africa and Asia, as well as from the blue-ice fields of Antarctica.
Another grouplet, closely related to the CR clan, has been proposed more recently around our unusal find Sahara 00182, and NWA 1152. Sahara 00182 was first thought to represent the first type 3 CR chondrite find, but a subsequent isotope analysis has shown it to have strong affinities to the CV group, too. Future studies, and hopefully new finds will have to show where this grouplet actually fits, and if it is distinct enough to be announced as a new main group, someday. As for this moment, all these meteorites are called "ungrouped", although there are obvious relations to each other, and to other groups of carbonaceous chondrites.