Carbonaceous chondrite - large slice (549 grams) of the Allende Meteorite. (Maine Mineral & Gem Museum collection, Bethel, Maine, USA)

Carbonaceous chondrites are dark gray to blackish-colored chondrite meteorites with a relatively carbon-rich matrix. The first large sampling of carbonaceous chondrites available to meteoriticists came with the 1969 fall of the Allende Meteorite. Before Allende, carbonaceous chondrite material was exceedingly rare. Allende has become the most heavily studied and the most famous carbonaceous chondrite.

Allende impacted on Earth at 1:05 AM on 8 February 1969. Its known strewn field trends southwest-to-northeast in the vicinity of the town of Allende in southeastern Chihuahua State, northern Mexico.

The slice shown above displays the internal structure & composition of the Allende carbonaceous chondrite. Allende has small, spherical to subspherical structures called chondrules (all chondrites have these). Allende also contains whitish, irregularly-shaped patches called CAIs (“calcium-aluminum inclusions”), composed of high-temperature Ca-Al-Ti silicates & oxides. The blackish, fine-grained, carbon-rich matrix consists of Fe-olivine & poorly graphitized carbon. A few tiny specks of metallic iron-nickel alloy also occur.