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Since the early days of meteoritics, different schemes have been
proposed to categorize the various meteorite samples in our collections. One
of the most popular of these classification schemes, originally developed by
Story-Maskelyne in the late 18th century, is based upon the primary composition
of each major group, dividing all meteorites into three main classes: stony
meteorites, stony-iron meteorites, and iron meteorites. Even though this scheme
is more than anachronistic, it's still widespread in literature as well as on
most meteorite related websites. |
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A New Classification Scheme
In our
Brief History of
Meteoritics (Part 3) we already outlined how Story Maskelyne's
original classification scheme was further refined and amended by Rose,
Tschermak, Brezina, Prior and many other pioneers of the young science
of meteoritics. Several subgroups were assigned to each of the three
primary classes, just to cope with the difficulties and discrepancies
that were brought about by this over-aged classification scheme – a
scheme that's nevertheless still common and widespread in the respective
literature, in publications, as well as on most meteorite-related
websites.
Modern meteoritics has a more sophisticated view and provides us with
classification schemes based upon the formation history, origin,
mineralogy, chemism, and also upon the more subtle isotopic compositions
of each meteorite class, clan, and group. According to contemporary
classification schemes, all meteorites can be basically divided
into two main categories:
Primitive meteorites, representing more or less
primordial matter that formed within the early solar nebula, and
which remained more or less unchanged for the last 4.5 billion years.
Most primitive meteorites belong to the class of
chondrites, named for the small spherical bodies or "chondrules"
that are so typical for the primitive meteorites.
Differentiated meteorites, on the other hand, have
been processed and changed during time, similar to the rocks on our own
planet which have been differentiated by igneous processing (i.e.,
melting, re-melting, and subsequent fractionation), and other
forces. Most differentiated meteorites belong to the class of
achondrites, although various types of
siderites, i.e., iron meteorites and stony-iron
meteorites, can also be regarded as genuine products of igneous
processing and planetary differentiation. Have a look at our
classification index for a detailed overview and
more information on the various meteorite classes and clans.
>> continue >> |
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Primitive Meteorite HaH 180
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(an ungrouped type 3.5 chondrite)
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Differentiated Meteorite NWA 1240
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(an anomalous basaltic eucrite)
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