[meteorite-list] Classification Criteria was Am I missing something here?

[Jeff Grossman]

This question periodically comes up, and the answer is: there isn't one.

The fact of the matter is that there is no 
"official" way of classifying meteorites (i.e., 
endorsed by a professional society or journal or 
other group).  When it comes to publishing 
classifications, it is up to the authors and, 
ultimately, editors to decide what to do.

The nearest thing to an "official" classification 
is what you see in the Meteoritical 
Bulletin.  But this only looks official.  Their 
Nomenclature Committee's (nomcom's) primary 
jurisdiction is only over meteorite names.  Their 
classifications are simply a matter of their own editorial policy.

The prevailing tradition on the nomcom is, 
however, a sensible one.  They normally publish 
classifications that are consistent with common 
usage among scientists.  They are normally 
conservative, meaning that they don't publish a 
new type of classification until it is obvious 
that at least a good part of the community has 
bought into it. They also mostly do not publish 
unusual classifications without reasonable 
evidence to support it. They use the literature 
as a guide to what criteria are necessary to 
demonstrate a given classification.  There is 
usually enough expertise on the nomcom to do this 
by inspection or with a little reading.  However, 
mistakes, oversights, and misjudgments can and do 
happen in this system, especially at the fringes of "common usage."

As for the general scheme used, check out the 
Wikipedia Meteorite Classification page, which I 
largely 
wrote. 
http://en.wikipedia.org/wiki/Meteorite_classification. 
For any given group, I may be able to give some 
insight into what criteria the nomcom has 
traditionally looked for.  The two main 
references cited there (numbers 2 and 3) are both 
good classification papers that give a lot of 
details on the properties of the various 
groups.  Unfortunately, both are chapters in 
expensive books, but pdf reprints can probably be obtained from the authors.

Jeff





At 04:16 PM 6/22/2008, Mr EMan wrote:
>The geek in me has always been curious as to the 
>actual classification criteria that a researcher 
>uses to make classification.  Does anyone have 
>them by name or PDF or hard copy?  Or volunteer 
>to explain the general scheme for different 
>classes? Sounds like fodder for a met-times 
>expose˘. Elton 
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Dr. Jeffrey N. Grossman       phone: (703) 648-6184
US Geological Survey          fax:   (703) 648-6383
954 National Center
Reston, VA 20192, USA