[meteorite-list] (Antarctica/desert weights) Meteorite Collecting Ban

From: j.divelbiss_at_att.net <j.divelbiss_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:32 2004
Message-ID: <20030810145942.B9BE55358F_at_pairlist.net>

Jeff and others,

Could the effects of glacial movements up against the mountains in Antarctica
actually keep a larger percentage of heavier pieces buried deeper in the ice
longer, while a larger number of smaller pieces would have surfaced first?

Since recovery teams have only been looking for 30 years...and
this "filtering" process has been going on for 10's of thousands of years,
maybe over time (a long time) the average size of the specimens found in
Antarctica would go up. Obviously the rate of finds from previously searched
areas would be a fraction of those early years.

Such a phenomena would skew the mass ratios back toward the desert material
sizes with the real number somewhere in between.

I would agree the number would be probably a lot closer to the present
Antarctica values. This generation of collectors may never know the answer.

John
>
> ><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
>
>
>
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Received on Sun 10 Aug 2003 10:59:40 AM PDT