Carbonaceous Chondrites - CB Group

Synonyms: Bencubbinites, Bencubbin-like chondrites

General: The carbonaceous chondrites of the CB group are named for their type specimen Bencubbin, a rather unusual meteorite that has been recovered in Australia in 1930. The CB chondrites are strange meteorites that often contain more than 50% nickel-iron.

Description: The CBs can be easily distinguished from all other carbonaceous groups due to their high metal content. They typically show mm-sized metal globules, and cm-sized chondrules, with the metal globules often distorted by shock or partial melting. All CB members recovered so far belong to petrologic type 3.

Mineralogy: Besides abundant free metal, CBs contain highly reduced silicates as well as armored chondrules similar to those found in the members of the CR group. Some members also contain CAIs. The CBs are further divided into the CBa subgroup, characterized by large metal globules and huge chondrules, and into the more metal-rich CBb subgroup with smaller chondrules, and metal globules.

Origin & Formation: It is more than probable that the CB chondrites, like all members of the CR clan, formed under different conditions in the same region of the primordial solar nebula, but it is also possible that they all come from one and the same parent body. In the latter case, 2 Pallas, the second largest asteroid of our solar system, would be a prominent candidate to be the original parent body of the meteorites of this clan.

Members: Only nine meteorites constitute this group: the type specimen Bencubbin, Weatherford, Fountain Hills, Gujba, NWA 1814, and NWA 4025 constituting the CBa main group, and the more metal-rich HaH 237, QUE 94411, and Isheyevo forming the CBb subgroup. Of all these members, Gujba is the only witnessed fall, and arguably the most beautiful CB chondrite in existence.