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Carbonaceous Chondrites - CM Group

CM Group Type Specimen Mighei - 0.5g Fragment

The CM Type Specimen: Mighei

(a small 0.5g broken fragment)

A Slice of CM2 Chondrite Murray - 0.482g

Slice of CM2 Chondrite Murray

(a thinly cut 0.482g partial slice)

Small Slice of the CM2 Chondrite Boriskino - 0.2g

A Small Slice of CM2 Boriskino

(a thinly cut ~0.2g partial slice)


Synonyms: Mighei-like carbonaceous chondrites

General: The CM chondrites are named for their type specimen Mighei, a meteorite that fell in Ukraine in 1889. The fact that CM chondrites contain water and complex organic compounds, such as amino acids, has caught the interest of science and the public, as well.

Description: Superficially, CM chondrites resemble the CI chondrites, and they also look a bit like a piece of tar on first sight. They also exhibit a low density, and a high porosity, but they mostly belong to petrologic type 2, i.e., they still show some well defined chondrules troughout their black matrix.

Mineralogy: With about 10% of water, CM chondrites contain less than the CI members, and they show less aqueous alteration so that some chondrules have been well preserved. Those chondrules consist of olivine and are scattered throughout the matrix. In that mixture of phyllosilicates and magnetite, similar to the matrix of CI chondrites, one also finds light-colored inclusions, such as CAIs. These high-temperature silicates are lacking in the CI group, and are quite typical for CM chondrites.

Origin & Formation: The CM chondrites are known to contain a wealth of complex organic compounds, such as amino acids. Because of this, some researchers have promoted the idea that the CMs might be of cometary origin. However, new comparisons of the reflectance spectra of meteorites and certain main belt asteroids yielded a close match, making asteroid 19 Fortuna a very good candidate to be the lost parent body of this peculiar class of carbonaceous chondrites.

Members: Excluding all probable pairings, about 100 CM chondrites are known. Some of them are famous witnessed falls, such as Mighei, Murchison, Murray, Boriskino, Cold Bokkeveld, and Nogoya.


Classification of Meteorites

> A New Classification Scheme
> Primitive Meteorites
> Differentiated Meteorites
> Classification Index

Chondrite Clans & Classes

> Carbonaceous Chondrites
   > CI Group  (Ivuna-like)
   > CM Group (Mighei-like)
   > CV Group (Vigarano-like)
   > CK Group (Karoonda-like)
   > CO Group (Ornans-like)
   > CR Group (Renazzo-like)
   > CH Group (High-Iron-type)
   > CB Group (Bencubbin-like)
   > Metamorphosed CCs
   > Ungrouped CCs
> Ordinary Chondrites
   > H Group  (High-Iron)
   > L Group  (Low-Iron)
   > LL Group (Low-Iron, -Metal)
   > Transitional OCs
> Other Chondrites
   > E Group (Enstatite)
   > R Group (Rumurutiites)
   > K Group (Kakangariites)
   > F Group (Forsterite)
   > Ungrouped Chondrites
> Metachondrites & PACs
   > Acapulcoites
   > Lodranites
   > Ureilites
   > Winonaites
   > Other Metachondrites

Achondrite Clans & Classes
Siderite Clans & Classes

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Copyright 2006-12 by N. Classen