Thanks very much Jeff.,
Your answer arrived while my post was sent. By
all means it better explains the complicated
situation regarding pairings than my poor trials.
Zelimir
At 18:01 18/01/2010, Jeff Grossman wrote:
I think I've answered this before, but again:
Yes, it would be great if all meteorites that
fell as a single shower (in a single field o'strewn) had a single name.
When a meteorite is found in Kansas or Germany
or Mexico, it's fairly easy to look in databases
and catalogs and find all the possible pairings
within, say, 50 km. If there are any of the
correct class, then it's ofter a simple matter
to compare the two meteorites and decide if they
are paired. NomCom rules actually require that
this is done, and if the probability of pairing
is high, a new name will not be granted to the new specimen.
When a new meteorite is found in, e.g., Oman or
Libya or Antarctica, things get much
harder. With hundreds of potential pairings
commonly existing, it is often very difficult or
even impossible to evaluate pairings. If the
type is rare enough it might be easier, but even
then the job can be burdensome on the classifier and the answer uncertain.
Once two meteorites are given a single name,
specimens become mixed up; it would be very hard
to separate two meteorites that were wrongly
given the same name. In light of all this, the
NomCom has decided that there is little benefit
to even trying to pair meteorites... names are
cheap and analysts' time is valuable. Therefore,
each specimen can and should be given a separate name.
From time to time, a situation comes up where a
very strong case can be made for pairing two
meteorites from a dense collection
area. Usually the motivation for doing so is
money: the owners don't want to donate 20 g or
20% type specimens of each of 10 valuable
specimens that are so obviously paired. In
this case, if they can make an overwhelming
case for pairing, including geographic
information, then the NomCom can grant a single
name to the multiple pieces. For NWA specimens,
this is not supposed to happen. The lack of
geographic information means that one can not
be certain of any potential
pairing. Therefore, the NomCom will not grant single names to multiple finds.
Of course, superimposed on all of this NomCom
policy is what collectors and dealers do by
themselves, unsanctioned by the Meteoritical Society.
Probably everybody knows of cases where somebody
obtained a new specimen and labeled it as an
existing meteorite from NWA or another dense
collection region. In addition, when NWA and
other meteorites are first classified, there
often are multiple pieces lumped
together. According to NomCom rules, these
groupings are only allowed when all the pieces
were picked up within a few m of each other or
fit together, but there is no guarantee that this is the case.
So that's the story. I hope this explains some things.
Jeff
On 2010-01-18 11:09 AM, Greg Catterton wrote:
I have often wondered and after some discussion
with others I wanted to get the community feeling on the issue of pairings.
If a meteorite say NWA 1877 for example is out
there and more is recovered and verified to be
the same material from the same strewnfield,
should the new material share the NWA number and the TKW be updated?
I have noticed many pairings with NWA 1877 and many other meteorites.
Same material with different numbers and TKWs listed.
Would it not be in the best interest to have
all the paired samples share on number? This
would surely cut the amount of NWA material by 1000 or more.
Why is this not done?
What is the process for pairing material to share the NWA number?
Is it up to the dealer or the person who did testing?
What affect would it have on value if something
with a listed TKW of 200g suddenly was paired
with the 3 other numbers assigned to the same
material and the TKW was pushed to 1kg or more?
Surely it would decrease as supply grew. Is this a concern for some?
I am trying to better understand the
politics/red tape that goes with this area.
Thanks, hope everyone is doing well.
Greg C.
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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
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Prof. Zelimir Gabelica
Université de Haute Alsace
ENSCMu, Lab. GSEC,
3, Rue A. Werner,
F-68093 Mulhouse Cedex, France
Tel: +33 (0)3 89 33 68 94
Fax: +33 (0)3 89 33 68 15
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