[meteorite-list] Fa and Fs values of LL meteorites

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Sat, 07 Apr 2007 08:21:29 -0400
Message-ID: <OFA2048B21.870C62B8-ON852572B6.0043E568_at_usgs.gov>

Mike,

For LL5 - LL6 chondrites, Fs values should be
between 22 and 27 mol%. Fs32 is unheard of, let alone Fs40.

In type 3 and 4 chondrites, Fs is not a
diagnostic classification tool. Pyroxene
equilibrates much more slowly than olivine, and
there is still significant heterogeneity in all
type 3s, whereas by high type 3 (e.g., 3.8-3.9),
olivine fayalite contents are nearly
homogeneous. Due to survival of enstatite
(grains with low Fs) coming from type I
chondrules, average Fs contents have not reached
equilibrium values in most type 3 chondrites, and
will be lower than the stated range. The is even
true for some type 4 chondrites!

Jeff

At 07:47 AM 4/7/2007, tett wrote:
>Hello List,
>
>Have just purchased a nice slice of a low TKW LL3. NWA 2461.
>
>The met bulliten lists Fayalite (mol%): 26.5?2.5
> Ferrosilite (mol%): 12.5?7
>
>
>The Met Bulliten also gives an official
>classification of an LL3. The encyclopedia of
>meteorites states that an LL3 should have a Fs
>value of 32-40 so how can this be grouped as an LL3? The Fa value fits.
>
>Looking at many other LL meteorites from the Met
>Base I see that the majority have Fs values well
>belwo the 32-40 level. I wonder if I am interpreting these incorreectly?
>
>Any help would be gratly appreciated.
>
>Cheers,
>
>Mike Tettenborn
>Owen Sound, Ontario
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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 07 Apr 2007 08:21:29 AM PDT