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The chondrites of the CR group are named for their type specimen
Renazzo, which fell in Italy in 1824. There are only about 15 CR
chondrites known, with Renazzo initially classified as a "type
II" CM2 chondrite. However, the CR chondrites are very
different from the CM group, although they also mostly belong to
petrologic type 2. Like the CM chondrites, they contain
hydrosilicates, traces of water, and magnetite. The main difference
is that they contain reduced metal in the form of nickel-iron and
iron sulfide of up to 10%. This metal is found in the black matrix
as well as in the large and clearly visible chondrules that make up
about 50% of the meteorites. Sometimes the orange-coloured
chondrules are "armored"; i.e. imbedded into small rims of
nickel-iron or iron sulfide. All this is typical for the chondrites
of the CR group, and it's quite easy to distinguish them from
members of other carbonaceous chondrite groups.
Scientists have searched for the origin of the CR chondrites,
comparing different reflectance spectra of asteroids with the
spectra of the known CR members. There's quite a good match between
the spectra of the CR members and one of the most prominent
asteroids in our solar system, 2 Pallas, the second largest asteroid
known. In addition, maybe we have other samples of this prospective
parent body since modern research suggests that two other groups of
carbonaceous chondrites are closely related to the CR chondrites -
the CH chondrites and CB chondrites or bencubbinites. Together they
form the so-called CR clan that either has its origin in one and the
same parent body or at least in a common region of the early solar
system in which they formed under similar, more reducing conditions.
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