[meteorite-list] nwa869

From: John Divelbiss <j.divelbiss_at_meteoritecentral.com>
Date: Thu Apr 22 10:00:05 2004
Message-ID: <000d01c2260d$66dec120$4b085a0c_at_0m824>

Hi Al and list,

Thank you again for being attentive to my ramblings. You and countless
others are close to, and more informed of the process and the expertise
given to the analysis of meteorites. I did not mean to trivialize this
process...and if I did offend anyone, I'm sorry. My nature, being a
mechanical consulting engineer, is to evaluate all situations with a bit of
skepticism and caution. It comes through on occasion with my meteorite
collection. So does my ignorance on the subject, but I'm learning.

As far as "looks" go when evaluating a particular piece, or when comparing
one to another...well that's all I've got, and the word of the seller and
it's evaluator. In the case the NWA's, the collection process as you
mentioned makes the identification process that much harder to be sure of a
given class/type. In the case of 869 and all its brother and sister #'s...I
would like to see a concerted effort to nail this one down. The wonderful
900 slices from Matteo deserve it, along with the unique 869 pieces Dean and
Mark have seen and offered with nice C clasts and brecciation, the same for
995 slices sold last winter, and let us not forget the beautiful slices of
904 and others (787 I believe) from the Hupes. All of these, and others as
Matteo suggested deserve an opinion of "are they from the same fall or
source?". I would appreciate it, and I'm sure many others would also. How it
would get done is a mystery to me. Maybe it could be project for a
university to study and comment on. How about it Ron?

Well I'm going to stop embarrassing myself on this one. Thanx all for
reading. Any identification information on any of the mentioned #'s would be
appreciated along the way. Thanx in advance.

John


----- Original Message -----
From: "almitt" <almitt_at_kconline.com>
To: "John Divelbiss" <j.divelbiss_at_worldnet.att.net>
Cc: "Matteo Chinellato" <mcomemeteorite2000_at_yahoo.it>; "dean bessey"
<deanbessey_at_hotmail.com>; <meteorite-list@meteoritecentral.com>
Sent: Sunday, July 07, 2002 8:23 PM
Subject: Re: [meteorite-list] nwa869


> Hi John,
>
> Probably in the past when ordinary chondrites were classified by oxidized
iron to iron
> metal percentages there was no doubt room for more error. Today using the
microprobe
> for chemical analysis, scientists are looking at about ten different items
and trace
> chemical signatures to distinguish the minute variation of the common
chondrites. To
> further help this out and isolate it more, the shock metamorphism is also
taken into
> consideration. Although no process is perfect I think there is a pretty
good handle on
> being able to distinguish individual falls these days using the processes
stated. Also
> weathering comes into play on these.
>
> With that said, I would think the bigger problem on a fall coming out of
the Sahara
> desert is whether some nomad decided to throw (or perhaps the rocks just
get mixed up
> in camel transit) into the lot and so we have a mixture of different falls
stated to
> be from one fall. As with meteorite dealers it is a matter of trust on
whom you are
> dealing with and if they are being honest with you or not. This isn't
meant to be a
> grind to those going over there an collecting these items.
>
> I don't think it is always a good idea to go by looks on meteorites (I
have many in my
> collection that are similar in appearance but from discrete falls and
finds) and until
> a detail analysis is done then it is really hard to say. As a rule with
time when
> these meteorites are looked at they may refine the classification. With
the break up
> of Hebe and back into a rubble pile we sample a variation of classes in a
single
> chondrite sometimes. I trust the researchers to be able to distinguish the
bulk matrix
> of these finds and produce a accurate classification. It is to their own
advantage
> when they do research on these to know the accuracy of classification on
the
> meteorites they are dealing with so they don't go the wrong direction on
understanding
> them. All my best!
>
> --AL
>
> John Divelbiss wrote:
>
> I just looked at the group I have and quite frankly it is not easy to say
> they are different materials. Even under the scope. Yet I see the reports
of
> L4 or L5 for NWA 869, L6 for 787, now L3.4/4 for 900, and similar
> suspicions for 995 (not 905 that I listed in earlier message). Thin
sections
> of each one may help...but as Dean has stated, his section may have thrown
> off the evaluation of his sample relative to its true petrologic type.
>
> All this makes me wonder about the process and "accuracy" of identifying a
> particular fall or find. As I understand it, the boundaries between H's
and
> L's can be somewhat blurred when metal and iron contents are in the
> transition percentage levels. All the more bewildering.
>
>
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Received on Sun 07 Jul 2002 07:24:10 PM PDT