Carbonaceous Chondrites - CH Group

Synonyms: High-iron-type carbonaceous chondrites

General: The CH chondrites are named for one of the typical properties of these meteorites. The “H” stands for “high iron” since CH chondrites contain up to 15% nickel-iron. The first CH member, Allan Hills 85085, has been recovered from Antarctica, and it can be regarded as the original type specimen of this group.

Description: Dark, metal-rich carbonaceous chondrites of different appearance. Besides their high abundance of metal, the CHs show sparsely distributed fragmented chondrules, only a few remaining intact. Most of these chondrules, as well as the less abundant CAIs, are very small. All CH chondrites that have been recovered, thus far, belong to petrologic types 2 or 3.

Mineralogy: As with the closely related CR chondrites, the members of the CH group contain certain amounts of phyllosilicates and other traces of aqueous alteration that took place during their history of formation. CAIs are also present within the fine grained silicate matrix.

Origin & Formation: Some scientists believe that the CH chondrites originally formed in close proximity to the Sun. This is reflected in the abundance of certain trace elements as well as in mineralogy. It is believed that the precursor material of the CH chondrites condensed in a very early stage from the hot primordial nebula – inside what is today the orbit of Mercury – and have been later transported to outer and cooler regions of the primordial solar nebula where they have been more or less preserved up to this day.

Members: There are only 12 CH members known if we exclude all probable pairings. Most of them have been recovered from the cold deserts of Antarctica, or from the hot deserts of Africa and Asia, such as Acfer 214, Acfer 366, or SaU 290. No witnessed CH chondrite fall has been recovered, thus far.