AW: [meteorite-list] Muonionalusta - Displacement Lines

From: Jörn Koblitz <koblitz_at_meteoritecentral.com>
Date: Thu Apr 14 11:03:58 2005
Message-ID: <492FFD0696089A4CB72BDBDCB2FC1A14029A42_at_server2000>

Dear Jeff,

Interesting feature! It certainly doesn't represent a grain boundary of former austenite crystals, as often seen in Gibeon pieces. In such a case, the kamacite lamellae would change their direction at the boundary due to the different crystal orientation of the former austenite grains (which, btw, had extensions rather in the meter than centimeter scale). I think, here we see shear bands, although unusual narrow and sharply defined. Such shear (or displacement) boundaries can be produced by shock loading at rather low temperature, when the Fe-Ni metal is fairly brittle, for example by impact with another meteoroid in space.

Cheers,
J?rn

> -----Urspr?ngliche Nachricht-----
> Von: meteorite-list-bounces_at_meteoritecentral.com
> [mailto:meteorite-list-bounces_at_meteoritecentral.com]Im
> Auftrag von Jeff
> Kuyken
> Gesendet: Donnerstag, 14. April 2005 15:06
> An: Meteorite List
> Betreff: [meteorite-list] Muonionalusta - Displacement Lines
>
>
> G'day List,
>
> I recently acquired a 306g Muonionalusta Half Slice which
> caught my eye for
> its unusual displacement/shock lines running through the
> etch. I remember
> recently that someone posted a pic of Gibeon(?) with a
> similar feature and
> there were theories that lines represented the boundary
> between the cooling
> of different areas.
>
> I believe the lines in the piece below are more likely from
> some sort of
> shock event as the pattern matches up like a jigsaw but I'd
> very much like
> to hear more opinions from others.
>
> http://www.meteorites.com.au/features/muonionalusta.html
>
> Thanks,
>
> Jeff Kuyken
> I.M.C.A. #3085
> www.meteorites.com.au
>
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Received on Thu 14 Apr 2005 11:08:09 AM PDT