Re: [meteorite-list] LL7 Chondrites

[Jeff Grossman]

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" <[EMAIL PROTECTED]>
To: "Adam Hupe" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
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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Dr. Jeffrey N. Grossman       phone: (703) 648-6184
US Geological Survey          fax:   (703) 648-6383
954 National Center
Reston, VA 20192, USA


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