[meteorite-list] Meteorite Collecting Ban
From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:31 2004
You are right; it is hard to compare the statistics. Many or most of the
described multi-fragment Saharan meteorites are those that decrepitated in
place in the much harsher weathering environment of hot deserts compared
with cold ones. Meteorites that formed strewn fields get just as many
numbers in the Sahara as in Antarctica (one per specimen). I grant you
that there are at least hundreds and maybe thousands of commercial stones
that don't ever get classified, as I said in my last posting... can anybody
estimate the actual number? You also have to remember that, according to
reports, many Saharan meteorites are intentionally broken up prior to being
described, which drives the statistics in the opposite direction.
I don't think total mass is a useful number because the statistics are
dominated by a few outliers. You really have to go to pairing-corrected
statistics. Lindstrom estimated that the average pairing group among
antarctic specimens is ~5, which lowers the total number of separate
Antarctic meteorites to about 4000. There are many pairings also among
commercially collected meteorites, although I don't know if anybody has
estimated the ratio in the same way as Lindstrom did. The average pairing
group among separately collected meteorites has got to be at least 3, I
would guess. So you take the 4000 or so commercial meteorites, and let's
allow an equal number of unclassified/undescribed stones, making
8000. Divide by my conservative 3, and you still have >2x as many unique
Antarctic meteorites as commercial ones. But let's face it... you can't
get even close to statements that were made indicating that 95% of new
meteorites are commercially collected ones.
As for rare meteorites, which I will define as non-ordinary-chondrites,
there are 1550 from Antarctica and 467 from commercial collections. So the
ratio of antarctic:commercial meteorites is 3:1 instead of the raw number
of 3.5:1 among total meteorites, enhanced by the "high-grading" that goes
on in the commercial sector. Commercial meteorites are still
overwhelmingly ordinary chondrites.
At 01:30 PM 8/8/2003, Starbits_at_aol.com wrote:
>Jeff Grossman wrote:
><70% of all known meteorites are Antarctic
> 20% of all known meteorites have been collected
> The remaining 10% include all the falls and sporadic
> finds throughout history.>
> I respectfully disagree. The naming conventions
>tilt those numbers significantly toward the antarctic
> In antarctic collecting every individual is given
>its own designation unless it is a fragment of a
>closely associated stone. All of these individuals are
>eventually classified even if 80% of a collection
>year are obviously related L5s.
> If every individual coming out of NWA were given
>its own designation the numbers would completely
>dwarf the antarctica numbers. In most cases a single
>stone is classified as representative of itself
>and possibly hundreds of other similar stones.
>NWA 801 CR and NWA 869 L5 are examples that come
> In addition while all the antarctic meteorites
>will eventually be classified this is not even
>close to being the case for hot desert meteorites.
>Due to lack of instrument time, money, and priorities
>on rarer meteorite types, many, if not most, ordinary
>chondrites from NWA will never be classified. That
>is not a criticism, just reality. Those NWA meteorites
>that are classified are predominantly the rarer types.
> A much more realistic determination would be a
>comparison of different rare types of meteorites. The
>mars compendium for instance lists 11 hot desert, 10
>antarctic, and 7 other mars meteorites for a ratio of
>39:36:25 vs the ratio above of 20:70:10. It would
>be interesting to see how the other rare meteorite
>types compare. Bernd?
> I don't know those comparisons but would guess
>the results would be closer to the mars ratios than
>the named classification ratio.
> Another comparison would be total mass. We know
>that NWA 869 has been estimated at 1500-2000kg alone.
>What is the mass of all the antartic meteorites?
>Meteorite-list mailing list
Dr. Jeffrey N. Grossman phone: (703) 648-6184
US Geological Survey fax: (703) 648-6383
954 National Center
Reston, VA 20192, USA
Received on Fri 08 Aug 2003 03:23:41 PM PDT