Carbonaceous chondrites or C chondrites are a class of chondritic

Chondrite

Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids...

 meteorite

Meteorite

A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

s 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

Allende meteorite

The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 1:05 a.m. on February 8, 1969, falling over the Mexican state of Chihuahua. After breaking up in the atmosphere, an extensive search for pieces was conducted and it is often described as...

, Murchison

Murchison meteorite

The Murchison meteorite is named after Murchison, Victoria, in Australia. It is one of the most studied meteorites due to its large mass , the fact that it was an observed fall, and it belongs to a group of meteorites rich in organic compounds....

, Orgueil, Ivuna, Murray, 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

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

, as well as organic compound

Organic compound

An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

s. They are composed mainly of silicate

Silicate

A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...

s, oxide

Oxide

An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....

s and sulfide

Sulfide

A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...

s, while the minerals olivine

Olivine

The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....

 and serpentinite

Serpentinite

Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...

 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

Solar nebula

In cosmogony, the nebular hypothesis is the most widely accepted model explaining the formation and evolution of the Solar System. There is evidence that it was first proposed in 1734 by Emanuel Swedenborg. Originally applied only to our own Solar System, this method of planetary system formation...

 from which the solar system

Solar System

The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

 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.

CI group

This group, named after the Ivuna meteorite, have chemical compositions that are close to that measured in the solar photosphere, neglecting gaseous elements. In this sense, they are chemically the most primitive known meteorites. They typically contain a high proportion of water (up to 22%), and organic matter in the form of amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s and PAH

Polycyclic aromatic hydrocarbon

Polycyclic aromatic hydrocarbons , also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH...

s. Aqueous alteration promotes a composition of hydrous phyllosilicates, magnetite

Magnetite

Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

, and olivine

Olivine

The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....

 crystals occurring in a black matrix, and a possible lack of chondrule

Chondrule

Chondrules are round grains found in chondrites. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids...

s. It is thought they have not been heated above 50 °C (122 °F), indicating that they condensed in the cooler outer portion of the solar nebula.

Five CI chondrites have been observed to fall: Ivuna, Orgueil, Alais, Tonk and Revelstoke. Several others have been found by Japanese field parties in Antarctica. In general, the extreme fragility of CI chondrites causes them to be highly susceptible to terrestrial weathering, and they do not survive on Earth's surface for long after they fall.

CV group

This group takes its name from Vigarano. Most of these chondrites belong to the petrologic type 3.

CV chondrites observed falls:

• Allende
  Allende meteorite
  The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 1:05 a.m. on February 8, 1969, falling over the Mexican state of Chihuahua. After breaking up in the atmosphere, an extensive search for pieces was conducted and it is often described as...
  
  
• Bali
• Bukhara
• Grosnaja
• Kaba
• Mokoia
• Vigarano

CM group

The group takes its name from Mighei, but the most famous member is Murchison. Many falls of this type has been observed. CM chondrites are well known to contain a rich mix of complex organic compounds.

CR group

The group takes its name from Renazzo (Italy).
The best parent body candidate is 2 Pallas

2 Pallas

Pallas, formally designated 2 Pallas, is the second asteroid to have been discovered , and one of the largest. It is estimated to constitute 7% of the mass of the asteroid belt, and its diameter of 530–565 km is comparable to, or slightly larger than, that of 4 Vesta. It is however 20%...

.

CR chondrites observed falls:

• Al Rais
• Kaidun
  Kaidun meteorite
  Kaidun is a meteorite that fell on 3 December 1980 on a Soviet military base near what is now Al-Khuraybah in Yemen. A fireball was observed travelling from the northwest to the southeast, and a single stone weighing about 2 kilograms was recovered from a small impact pit...
  
  
• Renazzo

Other famous CR chondrites:

• Dar al Gani 574
• El Djouf 001
• NWA 801

CH group

"H" stands for "high metal" because CH chondrites may contain up to as much as 40% of metal. That makes them the most metal-rich of any chondrite group. The first meteorite discovered was ALH 85085. Chemically these chondrites are close related to CR and CB groups. All specimens of this group belong only to petrologic types 2 or 3.

CB group

The group takes its name from the most representative member: Bencubbin. Although these chondrites contains +50% of nickel-iron metal, they are not classified as mesosiderite

Mesosiderite

Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic nickel-iron and silicate. They are breccias with an irregular texture; silicates and metal occur often in lumps or pebbles as well as in fine-grained intergrowths...

s because their mineralogical and chemical properties are strongly related with CR chondrites.
These chondrites were also called "bencubbinites".

CK group

This group take its name from Karoonda meteorite

Karoonda meteorite

The Karoonda meteorite fell to earth on November 25, 1930 at 10:53 pm near the South Australian town of Karoonda.The CK chondrites were named for this meteorite.-External links:**...

. These chondrites are closely related to the CO and CV groups.

CO group

The group take its name from Ornans (France). The chondrule size is only about 0.15mm on average. They are all of petrologic type 3.


Famous CO chondrite falls:

• Ornans
• Kainsaz
• Warrenton
• Moss
  Moss meteorite
  Moss is a carbonaceous chondrite meteorite that fell over the communities of Rygge and Moss in Østfold county, southeast southern Norway in the morning of midsummer day, July 14, 2006....
  
  
  

Famous finds:

• Dar al Gani 749

Organic matter

Ehrenfreund et al. (2001) found that amino acids in Ivuna and Orgueil were present at much lower concentrations than in CM chondrites (~30%), and that they had a distinct composition high in β-alanine

Alanine

Alanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 amino acids encoded by the genetic code. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...

, glycine

Glycine

Glycine is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG cf. the genetic code.Glycine is a colourless, sweet-tasting crystalline solid...

, γ-ABA

Aminobutyric acid

Aminobutyric acid may refer to any of three isomeric chemical compounds:* α-Aminobutyric acid* β-Aminobutyric acid* γ-Aminobutyric acid...

, and β-ABA but low in AIB

Aminoisobutyric acid

Aminoisobutyric acid may refer to either of two isomeric chemical compounds:* 2-Aminoisobutyric acid* 3-Aminoisobutyric acid...

 and isovaline

Isovaline

Isovaline is a rare amino acid that was found in the Murchison meteorite. It is an isomer of the biologically important amino acid valine. It may have analgesic properties....

. This implies that they had formed by a different synthetic pathway, and on a different parent body from the CM chondrites.
Most of the organic

Organic compound

An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 in CI and CM carbonaceous chondrites is an insoluble complex material. That is similar to the description for kerogen

Kerogen

Kerogen is a mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks. It is insoluble in normal organic solvents because of the huge molecular weight of its component compounds. The soluble portion is known as bitumen. When heated to the right...

. A kerogen-like material is also in the ALH84001

ALH84001

Allan Hills 84001 is a meteorite that was found in Allan Hills, Antarctica on December 27, 1984 by a team of U.S. meteorite hunters from the ANSMET project. Like other members of the group of SNCs , ALH 84001 is thought to be from Mars. However, it does not fit into any of the previously...

 Martian meteorite (an achondrite

Achondrite

An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystallization on or within meteorite parent bodies...

).

The CM meteorite Murchison

Murchison meteorite

The Murchison meteorite is named after Murchison, Victoria, in Australia. It is one of the most studied meteorites due to its large mass , the fact that it was an observed fall, and it belongs to a group of meteorites rich in organic compounds....

 has over 70 extraterrestrial amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s and other compounds including carboxylic acid

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

s, hydroxy carboxylic acids, sulphonic and phosphonic acids, aliphatic, aromatic and polar hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s, fullerene

Fullerene

A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and they resemble the balls used in association football. Cylindrical ones are called carbon nanotubes or buckytubes...

s, heterocycles, carbonyl

Carbonyl

In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups....

 compounds, alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

s, amine

Amine

Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

s and amide

Amide

In chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds. The term amide also refers to deprotonated form of ammonia or an...

s.

External links

• Carbonaceous Chondrite Images from Meteorites Australia - Meteorites.com.au