[meteorite-list] Pairing discussion/questions

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Mon, 18 Jan 2010 12:01:04 -0500
Message-ID: <4B5493D0.2060505_at_usgs.gov>

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

Received on Mon 18 Jan 2010 12:01:04 PM PST