[meteorite-list] LL7 Chondrites

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:54 2004
Message-ID: <5.1.0.14.2.20040325184827.01bae708_at_gsvaresm05.er.usgs.gov>

One of the reasons that type 7 ordinary chondrites are rare may be that
many researchers do not think the distinction between 6 and 7 is
significant and therefore never classify anything as type 7. As far as
anymeteorite called type "6/7" is concerned, don't forget that the slash in
a classification often means "I can't decide" and not
"transitional". Certain classifiers use lots of slashes and others never
use them at all.

jeff

At 04:30 PM 3/25/2004 -0700, Michael Farmer wrote:
>Dr Ted Bunch did the classification. I have to belive that he knows what he
>it doing. The pieces are up on my website right now.
>See them here
>http://www.meteoriteguy.com/nwa2092.htm
>http://www.meteoriteguy.com/nwa20922.htm
>Price is $30.00 gram today only.
>Mike Farmer
>----- Original Message -----
>From: "David Weir" <dgweir_at_earthlink.net>
>To: "Adam Hupe" <adamhupe_at_comcast.net>
>Cc: <bernd.pauli_at_paulinet.de>; <meteorite-list@meteoritecentral.com>
>Sent: Thursday, March 25, 2004 4:11 PM
>Subject: Re: [meteorite-list] LL7 Chondrites
>
>
> > Hey Adam,
> >
> > Yes, I agree with you. Very perceptive. The two types are mutually
> > exclusive based on the definition of Dodd. Type 7 ordinary chondrites
> > were originally defined by Dodd et al. (1975) according to specific
> > petrographic characteristics. They listed three metamorphic criteria to
> > distinguish between petrographic types 6 and 7:
> >
> > 1.the presence of poorly defined chondrules in type 6, but only relict
> > chondrules in type 7
> >
> > 2.low-Ca pyroxenes in type 6 contain no more than 1.0 wt% CaO (1.0 wt% =
> > ~1.9 mol% Wo), but more than 1.0 wt% in type 7; conversely, the CaO
> > content of high-Ca pyroxenes decreases from type 6 to type 7
> >
> > 3.feldspar grains gradually coarsen to reach a size of at least 0.1 mm
> > in type 7
> >
> > Perhaps this is one of those confused cases of classification in which
> > different labs call things by different terminology. Could they have
> > found both petrographic phases in the stone and used the slash to
> > indicate this? Who did the classification?
> >
> > Regards,
> > David
> >
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>
>
>
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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 25 Mar 2004 07:06:30 PM PST