or C chondrites
are a class of chondritic meteorites
comprising at least 7 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites. C chondrites represent only a small proportion (4.6%) of meteorite falls
Some famous carbonaceous chondrites are: Allende
, and Tagish Lake
Composition and classification
Carbonaceous chondrites are grouped according to distinctive compositions thought to reflect the type of parent body from which they originated. These are named after a prominent meteorite — often the first to be discovered — in the group.
Several groups of carbonaceous chondrites, notably the CM and CI groups, contain high percentages (3% to 22%) of water
, as well as organic compounds
. They are composed mainly of silicates
, while the minerals olivine
are characteristic. The presence of volatile organic chemicals and water indicates that they have not undergone significant heating (>200°C) since they formed, and their compositions are considered to be close to that of the solar nebula
from which the solar system
condensed. Other groups of C chondrites, e.g.
, CO, CV, and CK chondrites, are relatively poor in volatile compounds, and some of these have experienced significant heating on their parent asteroids.
This group, named after the......