They contain a high proportion of carbon (up to 3%), which is in the form of graphite , carbonates and organic compounds, including amino acids . In addition, they contain water and minerals that have been modified by the influence of water. The carbonaceous chondrites were not exposed to higher temperatures, so that they were hardly changed by thermal processes. Some carbonaceous chondrites, such as the Allende meteorite , contain calcium-aluminum-rich inclusions (CAIs). These are compounds that condensed out of the primordial solar nebula early on and are likely to represent the oldest minerals formed in the solar system .
Some primitive carbonaceous chondrites, such as the CM chondrite Murchison , contain presolar minerals , including silicon carbide and tiny nanometer-sized diamonds that apparently were not formed in our solar system. These presolar minerals were presumably formed during the explosion of a nearby supernova or in the vicinity of a pulsating red giant (more precisely: a so-called AGB star ) before they entered the cloud of matter from which our solar system was formed. Such star explosions release pressure waves that can condense matter clouds in their surroundings, which can lead to the formation of new stars and solar systems.
Based on their chemical composition, the carbonaceous chondrites are divided into the groups CI, CB, CM, CV, CO, CR, CK and CH.
- CI-Chondrites (C1), named after the fall of Ivuna, Tanzania , contain a high content of water (up to 20%) as well as numerous organic compounds such as amino acids. They were not heated above 50 ° C in the course of their existence and should have originated in the outer solar system. They may be components of former comets . The CI chondrites do not contain any visible chondrules as these were destroyed by the water.
- CB chondrites (Bencubbin, Australia ) consist of about 50% each of nickel-iron and silicates. Despite their high iron content, the meteorites are not counted among the stone-iron meteorites . Rather, due to their mineralogical properties and chemical composition, they are closely related to the CR chondrite. Representatives of this group are also known as " Bencubbinites ". The Bencubbinites may have formed in the interface between the nickel-iron core and the silicate mantle of a C-asteroid.
- CM chondrites (Mighei, Ukraine ) are similar to CI chondrites in terms of their chemical composition, but contain less water. They have clear chondrules and often inclusions of CAIs. The CM chondrites are also likely to have originated in the outer solar system.
- CV chondrites ( Vigarano , Italy ) are similar to common chondrites in terms of their chemical composition and structure. However, in contrast to these meteorites, they contain traces of water and organic substances. CV chondrites have clearly visible chondrules and numerous CAIs.
- CO chondrites ( Ornans , France) have a similar chemical composition to CV chondrites. However, they are darker and have very small chondrules and significantly fewer CAIs.
- CR chondrites (Renazzo, Italy) are similar to CM chondrites, but contain more nickel - iron and iron sulfide . Spectroscopic studies show a match with Pallas , the second largest asteroid in the main asteroid belt . The CR chondrites may have come from this celestial body.
- CK chondrites ( Karoonda , Australia ) have a high proportion of the mineral magnetite , which gives these meteorites a matt black appearance. CK chondrites contain chondrules of various sizes and occasionally inclusions of CAIs.
- CH-chondrites (high iron) contain a high proportion of nickel iron, often more than 50 percent by weight.
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