[meteorite-list] Meteorite Collecting Ban

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:32 2004
Message-ID: <5.1.0.14.2.20030809212854.01e750c8_at_gsvaresm02.er.usgs.gov>

><As for rare meteorites, which I will define as non-ordinary-chondrites,
> there are 1550 from Antarctica and 467 from commercial collections.>
>
>Let's refine the numbers a bit. Pretty much the start of hot desert
>collecting
>was in 1998. Of the numbers you quote above how many are since the start
>of 1998? Do the same pairing numbers Lindstrom estimated apply to the
>non-ordinary-chondrites? I don't have access to a database so Jeff if you
>could let us know I would appreciate it.
The pairing numbers are based on the abundances of non-OC's.

Since 1998, it's ~5:3 by number and 10:1 by mass in favor of commercial
meteorites for rare types. The total is ~500 rare meteorites.

><Meteorites that formed strewn fields get just as many
> numbers in the Sahara as in Antarctica (one per specimen).>
>
>I was under the impression that each specimen gets a separate designation
>in antarctica. If there was a witnessed fall in Antarctica such as bensour
>in Africa would it get a single name and entry in the catalog listing or would
>each stone found get a separate designation and entry?

Each stone in BOTH places gets a separate designation. However, as I said,
many Saharan meteorites are found as piles of rubble, so the reported
number of pieces is high for some. Of course there are a few recent
showers in Africa that have a single name. Observed falls in Antarctica
would be treated the same as anywhere else: no numbers.


>I can't make that estimate. That is one of the reasons that I asked about
>the total
>mass of Antarctic meteorites. Statistically it would be reasonable to
>assume the
>ratio of OCs to other meteorite types would be similar. Certainly
>differences in weathering will affect the numbers some, but in gross
>approximation they
>should
>be somewhat similar. If there is 10 or 100 times as much mass coming out of
>the hot desert there should be 10 or 100 times the rare stuff, or at least 2
>to 20 times. High mass strewn fields certainly could affect the statistics
>however neither region has many iron meteorites which would be most likely
>to affect the approximation. Stony falls aren't big enough that one fall
>should
>affect the gross approximation that much.

Well, the mass issue is messy. By and large, small stones are not
collected in Africa. Or at least, the ones that are never get looked at
unless somebody thinks they're special. This is why the mass ratio of rare
types is so much greater than the number ratio in the statistics
above. The median size of commercial stones of rare types is ~160 g,
whereas the same number for Antarctic ones is ~18 g. In Antarctica, all of
the gram-sized stones have been collected (including many "main masses" in
this size range!). So you're looking at an incredibly size-biased Saharan
collection, and an Antarctic collection that more closely represents what
actually falls. I think the Antarctic collection has about the correct
number of irons (after correction for pairing) based on fall statistics
. The Saharan material has been scavanged by man over the centuries, and
the irons are apparently long gone.

Of course, in terms of importance to science, the high mass of
African/Omani meteorites is not the important issue. Most specimens of
these that are deposited in scientific collections now weigh 20 g or
less. This is a very hard number to get stats on, but I counted the Libyan
and NWA's in the latest bulletin and found that the median size of rare
meteorites deposited in collections is on the order of 15 g, which is
actually about the same as the median Antarctic size. The rest is
eventually destroyed as far as many scientists are concerned, or at least
badly compromised. We can do a lot with a few grams (as we have always
done with Antarctic meteorites), but future researchers will have precious
little material to study, and nobody gets the chance to study hand-sample
scale features once the specimen is sliced into a million bits. For
Antarctic meteorites, this is the hand we were dealt. But for warm
deserts, it is a sociological phenomenon. These are the reasons why many
scientists resent commercial meteorite ventures. To me, this situation is
a compromise that we can all live with, considering the bad alternatives on
both sides (read my editorial in MAPS from 2 years ago).

On the subject of this whole thread, I don't know of very many scientists
who would say something as silly as "commercially collected meteorites have
little scientific value." Where in the world did this idea come
from? Somebody should count the abstracts from Muenster and see how
scientists "voted with their feet" on this idea. The main problem some
museum scientists have is caused by their worry that many of these
meteorites are smuggled out of their countries-of-origin, and therefore
adding them to their collections is unethical, if not illegal.

jeff

>Eric Olson
>http://www.star-bits.com
>
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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 Sun 10 Aug 2003 09:49:20 AM PDT