[meteorite-list] NWA 2918 CO3.0 reclassification AND Most Current/Accurate Meteorite Classification

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Sat Jul 22 20:11:57 2006
Message-ID: <7.0.1.0.2.20060722192957.0385b500_at_usgs.gov>

Two replies for the price of one:

1) NWA 2918. An abstract is not peer reviewed, however I'll stand by
my classification of NWA 2918. It's a very nice meteorite, but more
metamorphosed than 3.0. There are actually three CO3.0
chondrites. In addition to ALHA77307, Y-81020 and Colony are both
3.0, but Colony is so horribly weathered that it is scarcely worth mentioning.

2) What is the most current and accurate classification? Let me editorialize.

* The Catalogue of Meteorites online database used to be the best,
but it has simply not been updated frequently enough to keep up with
current science or new
meteorites. http://www.nhm.ac.uk/research-curation/projects/metcat/

* MetBase, which is not an online resource, is very current (usually
within 6 months), but in a few cases the classifications have been
updated in a less conservative way than I would
do. http://www.metbase.de/. It is an excellent resource.

* The original Meteoritical Bulletin classifications were simply
initial evaluations, so they are not to be trusted down the road.

* In the MetBull database, you will find a "recommended"
classification. These are largely taken from MetBase plus NomCom,
ANSMET, and NIPR data releases that postdate the latest edition of
MetBase. However, they are tempered by me. For example, if you look
up Tagish Lake, MetBase will tell you it's CI2, which was a
speculative statement in the initial description and a few
abstracts. The NHM Catalogue database just says C2, which is not
very helpful. If you read the literature, especially Zolensky's big
2002 paper in MAPS, it's pretty clear that a conservative conclusion
would be C2 ungrouped. So when I think MetBase went too far, as in
this case, I back it off a bit in the recommendation. In other
words, I am the editor of this database. You can always see the
original MetBull, the NHM, and the MetBase classification as well.
http://tin.er.usgs.gov/meteor/

* The new Encyclopedia of Meteorites is a work in progress. It gets
a lot of information directly from the MetBull database (in real time
now!), but it also lists a number of meteorites that are not formally
named or classified. You take your chances with these, as far as I'm
concerned. http://www.encyclopedia-of-meteorites.com/login.asp

If there's anything else out there online, I don't know much about
it. So there you have it.

Jeff

At 07:25 PM 7/22/2006, David Weir wrote:
>Hello Adam,
>
>I just wanted to bring to your attention the new MetSoc abstract
>written by Jeff Grossman et al. which disputes the initial
>classification of your CO3.0 NWA 2918, and argues that it's actually
>a CO3.1. I see that you still have this meteorite for sale on ebay
>as a CO3.0 and I'm sure you'll want to include this correction in
>your accompanying description (see below) for the benefit of the
>potential buyer. Obviously the new stricter standards to which you
>refer are not the strictest in use. When I bought my two small
>pieces of this one from you I admit I was speculating that it would
>hold up as a rare CO3.0 comparable to the only known CO3.0,
>ALHA77307, especially based on your description, but a CO3.1 is not
>bad either. The abstract can be viewed here:
>
>http://www.lpi.usra.edu/meetings/metsoc2006/pdf/5283.pdf
>
>Since this was not published in a peer-reviewed journal perhaps Jeff
>Grossman is wrong, time will tell. Keep up the great work in finding
>us new rare material Adam.
>
>Regards,
>
>David
>meteoritestudies.com
>--------------------------------------------
>BRAND NEW-NWA 2918 Intensely Rare CO3.0 Meteorite .752g
>
>.752 gram end cut of Northwest Africa 2918, a CO3.0, S1, W2 Ornans
>type carbonaceous chondrite found 2005 in the Sahara desert. The
>perfect 3.0 subtype is exceeding rare among all types of chondrites
>but is the ultimate rarity among CO type chondrites with only one
>other non-Antarctic meteorite listed in the Catalog of Meteorites
>which is named Colony. NWA 2918 was graded using the new stricter
>standards so it is now the only perfect 3.0 in private hands that I
>am aware of since Colony was slightly downgraded to a 3.0-3.1 using
>the same new standards. The only other perfect 3.0 is an Antarctic
>piece named ALH 77307, which is not available to the public. Only
>one stone was found and it weighed only 237 grams making it an
>intensely rare specimen.
>
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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 Sat 22 Jul 2006 08:11:41 PM PDT