[meteorite-list] Chondritic parent bodies: Clarification

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu, 10 Sep 2009 07:29:27 -0400
Message-ID: <4AA8E317.9030509_at_usgs.gov>

Yes, it's the same idea. Usually, the L(LL) notation is used for highly
unequilibrated (petrologic type type 3.0-3.4) ordinary chondrites.
I've been studying these things for decades and I still don't know of
any way to distinguish a low type L from LL chondrite using an optical
microscope, SEM, or electron microprobe. Even O isotopes don't always
tell you. You have to do bulk chemistry, which is rarely done anymore
on OCs, and certainly not in the initial classification.

Take, for example, one that I've worked on: NWA 1756. It is classified
as LL3.10. In my opinion it could just as easily be an L3.10, as nobody
(to my knowledge) has done the chemistry to provide a definitive answer.
To me, such meteorites are all uncertain. If I was the original
classifier of this meteorite and I thought the properties looked more
LL-like, I'd have called it LL(L). If I was totally unsure, I'd have
called it L/LL. The 3.10 pet-type, on the other hand, is independent of
chemical group.

This brings up one last issue. If NWA 1756 could be called L/LL because
a classifier cannot tell which it is, but Bjurb?le is called L/LL
because it is truly intermediate, then this is two completely different
uses of the same symbol. John Wasson and I want to propose a new
nomenclature: Bjurb?le should be changed to L^LL4, where the caret
indicates known intermediate properties. One day we'll get around to
proposing it.

Jeff G.

Jeff Kuyken wrote:
> And there are also quite a few with L(LL) for example. I always
> thought this was the classifier saying they were not totally sure for
> some reason but their 'best guess' was the first class outside of the
> brackets. Is this similar to L/LL?
>
> Cheers,
>
> Jeff
>
>
> ----- Original Message ----- From: <bernd.pauli at paulinet.de>
> To: <Meteorite-list at meteoritecentral.com>
> Sent: Thursday, September 10, 2009 6:22 AM
> Subject: [meteorite-list] Chondritic parent bodies: Clarification
>
>
>> Tracy writes:
>>
>> "Oog. I agree with Bernd; classification is currently a mess."
>>
>> Sorry, I forgot the inverted commas => " ... "
>>
>> Those were Jeff's remarks / comments!
>>
>> Bernd
>>
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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 Thu 10 Sep 2009 07:29:27 AM PDT