[meteorite-list] Very strange Nickel-Iron (and Troilite) structure in a NWA chondrite (answer)

From: Jason Utas <meteoritekid_at_meteoritecentral.com>
Date: Tue, 19 Oct 2010 15:54:51 -0700
Message-ID: <AANLkTimkeMGBT3ZZnd5aBD-A+OXsrb3ApgY0bcJ9+kL2_at_mail.gmail.com>

Hello All,
I replied in private, and resent my post to the list already, but
apparently it didn't go through the first time.

I've seen several identical inclusions in shocked and melted
chondrites; the darker material is troilite (iron sulfide) and the
lighter material is nickel-iron. ?It has nothing to do with being the
blebs possessing a "precursor" widmanstatten pattern; the lighter and
darker areas are simply a dendritic intergrowth of nickel-iron and
iron sulfide. And that makes sense - in a shock melt, those elements
would tend to aggregate due to their shared chemical affinities.

Every metal inclusion in the lighter portion of this stone is
similarly structured:

http://picasaweb.google.com/MeteoriteKid/Chondrites#5417248216358065954

SEM photo of one of these inclusions from the same stone (NWA 3196):

http://picasaweb.google.com/MeteoriteKid/Chondrites#5529579598689715906

I'll leave the SEM photo on picasa for a few days - if anyone wants to
see the element map of the same thin section, I'll be able to get
ahold of it in a few months - I left my hard copy at home and will
need to scan it.

The element maps that we made of the same thin section agreed with our
hypothesis that the darker areas were in fact iron sulfide - the dark
regions were rich in sulfur and depleted in iron and nickel relative
to the lighter areas.
Some of my other photos also show fracturing and chipping in the
darker regions (typical for low-to-moderately shocked troilite), which
metallic iron would never show.

Regards,
Jason


On Sun, Oct 17, 2010 at 4:10 PM, m42protosun <m42protosun at t-online.de> wrote:
>
> Hello lists, with my new Bresser microscope I have detected a structure in metalflakes which I can not explain. Has any one seen such a structure in meteorites or documentation where it is explalned?
> Look at
>
> http://s345.photobucket.com/albums/p384/m42protosun/Bubble%20iron/
>
> m42protosun
>
>
>
>
>
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Received on Tue 19 Oct 2010 06:54:51 PM PDT