[meteorite-list] Mineral migration pattern in NWA 2977 lunar fleck of iron

From: STARSANDSCOPES at aol.com <STARSANDSCOPES_at_meteoritecentral.com>
Date: Sun, 21 Sep 2008 14:04:54 EDT
Message-ID: <d2e.28e29d32.3607e6c6_at_aol.com>

Hi list,

This is not just a plug to look at my micrographs of NWA 2977 Lunar.

I have noted a pattern (in some small iron flecks) that looks like a small
version of Widmanstatten Pattern or at least some kind of mineral migration
pattern. This is not in all meteorite iron. I note it rather infrequently.
I am speaking about iron in stone meteorites, not iron meteorites!

These patterns are quite small as the magnification is often approaching
2000X. Revealing this pattern requires a high polish (I use a 1/4 micron
diamond slurry) and reflected cross polarized light.

Recently, in a NWA 2977 lunar gabbro thin section I spotted an iron fleck
with this pattern. This was a first for me in a Lunar. Not the first iron
fleck in a Lunar, but the first with a pattern.

What is the consensus? Is it a caused by a process similar to what creates
Widmanstatten? I have had it dismissed as a shock structure but I don't buy
into that idea. It is my idea that heating of the iron removes evidence of
the pattern just as occurs with Widmanstatten and that is why it is rather
rare.

This September Meteorite Times has images of this NWA 2977 iron.
http://www.meteorite-times.com/meteorite_frame.htm In the menu to the left click on
Micro Visions. Please let me know what you think.

Thanks, Tom Phillips




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Received on Sun 21 Sep 2008 02:04:54 PM PDT