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Carbonaceous Chondrites

Murchison, Australia, carbonaceous chondrite, CM2

Carbonaceous (C) chondrites are some of the most complex of all meteorites. They are rare, primitive and contain organic compounds. Most importantly they contain water-bearing minerals which is evidence of water moving slowly through their interiors not long after formation.

C chondrites are further divided according to chemical and mineralogical differences into the sub-classes CI, CM, CV, CO, CK and CR. These sub-classes are named for the type specimen of each group, Ivuna, Mighei, Vigarano, Ornans, Karoonda and Renazzo respectively.

The fine-textured, small chondrule attributes of the carbonaceous chondrite Isna, Egypt are displayed in this image

Like the ordinary chondrites, C chondrites also have petrologic grade designations. In addition to grades 3 to 6, indicating increasing heat metamorphism of chondrules, grades 2 and 1 indicate increasing metamorphism of the meteorite by water. Carbonaceous chondrites are the only meteorites known with petrologic grades 1 and 2.

Two carbonaceous chondrites, Allende and Murchison, are of particular interest to scientists and, curiously, both fell in 1969, but on opposite sides of the world.

Fusion-crusted fragment, Orgueil, France, Carbonaceous chondrite, CI1

Allende, Mexico (14K GIF) is classed as CV3 and represents some of the oldest known matter. The meteorite formed 4.56 billion years ago and contains interstellar grains within calcium/aluminum rich inclusions (CAIs). Interstellar grains are remnants of a prior star that lived out its life and exploded before the formation of our Sun. It is possible that this explosion was the trigger for the formation of our solar system.

Section of the Allende, Mexico CV3 meteorite.

Murchison, Australia, image at the top of the page, is a CM2 chondrite and believed to be of cometary origin because of its high water content, 12%. To date 92 amino acids (the building blocks of protein) have been found in Murchison. Only nineteen of them are found on Earth.

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