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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