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

[Jeff Grossman]

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