[meteorite-list] Stones with High Troilite, Low Metal

From: Carl Agee <agee_at_meteoritecentral.com>
Date: Tue, 28 Jun 2011 17:44:37 -0600
Message-ID: <BANLkTi=wQ4rU6fpdxgu5MA-5v6s60Vj8pA_at_mail.gmail.com>

Hi Pete,

I sent you some email attachments with backscatter electron images of
NWA 6588 done with our electron microprobe. Sorry, I need to find the
time to put some photos on the EoM, but not yet registered! I'm am
having our website and the IOM Meteorite Catalog upgraded right now,
so many photos of our collection soon the come.

In the photos that I sent, you can see the bright sulfides are
actually two different minerals, usually in contact with each other.
The pentlandite is Ni-rich iron sulfide and the "pyrite" is just iron
sulfide (FeS2 pyrite formula, not FeS troilite). The image "Relict
Chondrules 2" shows a lower magnification of the overall microscopic
texture of NWA 6588. All the bright spots are sulfide. You can see the
porphyritic olivine chondrule in the upper right and the in the lower
left is part of a barred olivine chondrule.

Because of the small size of the sulfides, the best way to determine
which iron sulfide(s) is present is by electron microprobe
quantitative analysis or by EDS on and SEM. I was actually quite
surprised when NWA 6588 turned out not to have troilite!

Best regards,

Carl Agee

-- 
Carl B. Agee
Director and Curator, Institute of Meteoritics
Professor, Earth and Planetary Sciences
MSC03 2050
University of New Mexico
Albuquerque NM 87131-1126
Tel: (505) 750-7172
Fax: (505) 277-3577
Email: agee at unm.edu
http://epswww.unm.edu/iom/pers/agee.html
On Tue, Jun 28, 2011 at 4:10 PM, Pete Pete <rsvp321 at hotmail.com> wrote:
>
>
>
> Dear Carl, Doug, and List,
>
>
>
> Carl, your classification of NWA 6588 reads very close to this one! Thank you for that link.
>
>
>
> Am I sure the sulfide in mine is all troilite? Absolutely not. Is there a test for it that I can do?
>
> I'm only going by my experience of what I've seen in books, the net, and the classifieds and non-classifieds that I have here.
>
> The lack of obvious nickel or iron and (what I think is) lots of troilite is what piqued my interest enough to ask if there was similar out there.
>
> You indicated in your classification that this was indeed unusual.
>
>
>
> Since there aren't any photos of NWA 6588 online yet, I'd appreciate your viewing these of mine:
>
>
>
> http://tiny.cc/ymksq
>
> http://tiny.cc/ymksq
>
>
>
> https://skydrive.live.com/?cid=B8A3E8CAAAC69704&id=B8A3E8CAAAC69704%21114&sc=documents
>
> in case the tiny doesn't work.
>
>
>
> Anything that appears reflective, white, or gold coloured is what I suspect is troilite.
>
> The sulfide appears to be sprinkled into individual grains further away from concentrated areas.
>
> I didn't try to Photoshop the true colour back in, but a dark khaki grey is more accurate for the matrix.
>
>
>
> As with any meteorite, the pictures don't do the actual beauty justice ;)!
>
>
>
> Cheers,
>
> Pete
>
>
>
>
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>
>
>
>
>
> ----------------------------------------
>> Date: Mon, 27 Jun 2011 06:47:53 -0600
>> From: agee at unm.edu
>> To: meteorite-list at meteoritecentral.com
>> Subject: [meteorite-list] Stones with High Troilite, Low Metal
>>
>> Hi Pete,
>>
>> What about an LL -- with some desert weathering? The low-low metal can
>> be converted to small Fe-oxides or veins.
>>
>> I recently classified Northwest Africa 6588 (LL6-an), that had only
>> trace amounts of Fe-Ni metal. The ubiquitous sulfides present are
>> pendlandite and stoichiometric pyrite. See metsoc 2011 abstract:
>> http://www.lpi.usra.edu/meetings/metsoc2011/pdf/5418.pdf
>>
>> Are you sure the sulfide is all troilite?
>>
>> Carl Agee
>>
>> --
>> Carl B. Agee
>> Director and Curator, Institute of Meteoritics
>> Professor, Earth and Planetary Sciences
>> MSC03 2050
>> University of New Mexico
>> Albuquerque NM 87131-1126
>>
>> Tel: (505) 750-7172
>> Fax: (505) 277-3577
>> Email: agee at unm.edu
>> http://epswww.unm.edu/iom/pers/agee.html
>>
>> -------------------------------------------------------------
>> Message: 13
>> Date: Mon, 27 Jun 2011 00:31:45 -0400
>> From: Pete Pete <rsvp321 at hotmail.com>
>> Subject: Re: [meteorite-list] Stones with High Troilite, Low Metal
>> To: <mexicodoug at aim.com>, <meteoritemike at gmail.com>, meteoritelist
>> meteoritelist <meteorite-list at meteoritecentral.com>
>> Message-ID: <bay153-w42304EFE707206467A6876F8570 at phx.gbl>
>> Content-Type: text/plain; charset="iso-8859-1"
>>
>>
>> Thank you all for your responses.
>>
>> You're right, Doug, too ambiguous a question.
>>
>> I have an unclassified NWA, which I've sliced and polished. There are
>> so many interesting features that it is the type that you never get
>> tired of looking at under the microscope.
>>
>> It has what appears to be the remains of transformed chondrules; four
>> total in about 2cm^2 surface.
>>
>> Three look like bit-remains of brecciated chondrules, grey and white.
>> The other looks like a typical barred chondrule that has become
>> completely crystallised, and has the schiller effect.
>>
>> A very fine grained matrix, no observable free metal as in
>> nickel/iron, and what *appears* to be typical troilite scattered
>> throughout.
>> Low attraction to a neodymium magnet.
>>
>> The fusion crust is relatively fresh, with no chert.
>> Quite different from the others I've got, so I was hoping to read and
>> possibly view images of similar.
>> As I said, there are no silver metal flecks, only the dull yellow
>> troilite-looking areas.
>> Is it possible for nickel/iron to have this appearance, too? I had
>> mentally eliminated that due to the low magnet attraction, but I've
>> got lots to learn.
>>
>> Cheers,
>>
>> Pete
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Received on Tue 28 Jun 2011 07:44:37 PM PDT