Carbonaceous chondrite is any stony meteorite or asteroid containing material associated with life (e.g., hydrocarbons, amino acids, and forms resembling microscopic fossils) and for which some researchers have postulated an extraterrestrial biological origin. Instead of containing the anhydrous silicates found in most chondrites, the carbonaceous types have claylike hydrous silicate minerals. They also contain carbonate and sulfate minerals, iron oxides, and sulfur. Magnesium sulfate is found in narrow veins; and since it is water soluble, carbonaceous chondrites disintegrate rapidly because of weathering.
They comprise about 3 percent of all the meteorites collected after being seen in flight. Their texture, similar to that of the terrestrial rocks called volcanic tuffs, indicates that they have been repeatedly fragmented and re-cemented.
Excerpt from the Encyclopedia Britannica without permission.