Ungrouped Carbonaceous Chondrites

Some carbonaceous chondrites don’t fit easily into the established groups, although they can be identified as members of the clan of carbonaceous chondrites. They are usually designated as CC ungrouped or CC UNG and they probably represent other parent bodies 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.

Unique samples: A good example for a CC ungrouped is the witnessed fall of Tagish Lake, a primitive type 2 chondrite that fell in Canada in 2000, and which initially has been thought to represent the first type 2 member of the CI group. However, studies have shown that it is unrelated to the CI group, and that it probably has his origin on another, so far unsampled parent body, most likely a D- or T-type asteroid.

Grouplets: Amoung meteoriticists it’s an unwritten law in the naming of 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, e.g., is named for the meteorite of Coolidge that was found in Kansas in 1937. Including Sahara 00177 and Loongana 001, there are three other CCs designated CC UNG, 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 identified in the wealth of new finds from the hot deserts of Africa and Asia, as well as from the ice fields of Antarctica.

Another grouplet, closely related to the established CR clan, has been proposed more recently around Sahara 00182, and NWA 1152. Sahara 00182 was first thought to represent the first pristine type 3 CR chondrite find, but a subsequent isotope analysis as well as additional studies have shown it to have strong affinities to the CV group, too. Future studies, and hopefully new finds, will have to show where this small new grouplet fits, and if it is actually distinct enough to be announced as a new main group, someday.