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

From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Mon, 27 Jun 2011 06:28:50 -0400
Message-ID: <8CE02CC1F2677B7-1044-31331_at_webmail-m163.sysops.aol.com>

Jason says:

"You may well be right, but since troilite is typically present in
rather minor concentrations in most meteorites, I have the feeling
that they are not depleted in it relative to most other types...but I
could be wrong."

"So, troilite is always pyrrhotite, but pyrrhotite isn't always
troilite."

Hi Jason,

It is clearer IMO to think of troilite simply as the stoichiometric
Fe-S endpoint of pyrrhotite; Getting polyphyletic or not is best lefts
to cladists!

I'm not sure of the utility of the thought you have regarding
"depleted":

It is much better to think of this as a dynamic evolution to form the
Metal-sulfides. The RELATIVE amount of stable sulfides to sulfates and
oxides begins to tell good clues on the environment of formation; just
as a possible rich sulfurous cloud condensate is postulated on origin.
Further, the RELATIVE amount amount of troilite to pyrrhotite being
quite low and in many cases nearly trace, gives more clues since it is
a troilite is saturated state and has physical implications. The fact
that R chondrites are so rich in sulfur yet RELATIVELY poor in troilite
is the reverse of what is expected (Except for Dr. Rubin's ALH85151
which would be exciting if he has a theory to explain it, otherwise
just an outlier to keep in mind). So regardless of what is in the
online literature, if you want to begin forming hypotheses on any of
the interesting qualities and origins of R chondrites, the least
interesting thing is to compare across other classes as you suggest
without a theoretical framework of what's going on within this stinky
meteorites. (Sure, if you just have the rock under the loop it might be
of some utility to get oriented but that still isn't convincing to me).

"- The only source I found in my short quest for knowledge that
bothered to note how much "troilite" is (typically) present in
R-chondrites is the NAU website."

Bothered to note? - things like this are important to recognize as
likely an open research opportunities - not dirt behind the
refrigerator! I'm betting that the 'omission' is because that's easier
than trying to explain something we Olympians don't have a clue about
(or it is someone's R chondrite Nobel prize theory secret still under
development), at least in the literature quickly available to us. A
good place to check on the simple compositional question of being
relatively troilite poor would be the analysis of the type specimen,
Rumuruti ... where I'm sure it was noted. If not there, my next
convenient bet would be David Weir's fantastic meteoritestudies.com
site.

Kindest wishes
Doug





-----Original Message-----
From: Jason Utas <meteoritekid at gmail.com>
To: MexicoDoug <mexicodoug at aim.com>
Sent: Mon, Jun 27, 2011 4:01 am
Subject: Re: [meteorite-list] Stones with High Troilite, Low Metal


Hello Laurence, Doug, All,

>From an NAU site about R-chondrites:

"sulfide rich: pyrrhotite and pentlandite very common, minor troilite;
pentlandite commonly contains Cr up to 2 wt%, troilite may contain Ni
up to 3 wt%"

http://www4.nau.edu/meteorite/Meteorite/Rumuruti.html

Which raised the question -- what is troilite and what is pyrrhotite?

"Pyrrhotite is an unusual iron sulfide mineral with a variable iron
content: Fe(1-x)S (x = 0 to 0.2). The FeS endmember is known as
troilite."

http://en.wikipedia.org/wiki/Pyrrhotite

So, troilite is always pyrrhotite, but pyrrhotite isn't always troilite.

I don't know whether the sulfides in R-chondrites is primarily FeS
where S=1 or S<1, but the distinction is rarely made except in
academic circles. In fact, none of the following top hits goes into
any depth regarding pyrrhotite vs troilite concentrations in
R-chondrites. These were the first three I found:

http://adsabs.harvard.edu/full/1994Metic..29..275S

http://adsabs.harvard.edu/full/1994Metic..29..255R

http://www.sciencedirect.com/science/article/pii/S0009281911000237

- The only source I found in my short quest for knowledge that
bothered to note how much "troilite" is (typically) present in
R-chondrites is the NAU website.

You may well be right, but since troilite is typically present in
rather minor concentrations in most meteorites, I have the feeling
that they are not depleted in it relative to most other types...but I
could be wrong.

For the purposes of Pete's visual observations, I think we can assume
that he meant sulfides in general, since I doubt he has the analytical
capability to tell between FeS (S=1) or FeS (S = 1 to 0.8).

When I saw Pete's note, I immediately thought of R-chondrites,
too...though I wonder if his stone might not be an LL-chondrite. We
have a few R's, and when poked with a neodymium magnet, the pull is
*barely* discernible, to the point that I might call them entirely
non-magnetic if I weren't being careful.

Regards,
Jason


On Sun, Jun 26, 2011 at 6:15 PM, MexicoDoug <mexicodoug at aim.com> wrote:
>
> Hi Laurence
>
> Sulfur stinky yes, I don't think R chondrites are considered troilite
rich -
> are they not comparatively troilite poor? That's why I asked why he
wasn't
> after pentlandite (and pyrrhotite) as well. The question is pretty
useless
> trivia without more information about what the asker is after ... ,
Sulfur
> (check), Sulfides (check), Low free metals, terrestrial weathering,
> different alterations, they are all bundled up together. I mean, R
> chondrites are loaded with metal but it was oxidized after the
formation,
> right? Considering, they are quite troilite poor unless the objective
is
> sulfur-rich meteorites and not after troilite after all... maybe
perhaps who
> knows
>
> Best Doug
> (Thinking of Mrs. Pennyfeather now!)
>
>
> -----Original Message-----
> From: Laurence Garvie <lgarvie at asu.edu>
> To: meteorite-list at meteoritecentral.com
> <meteorite-list at meteoritecentral.com>
> Sent: Sun, Jun 26, 2011 8:15 pm
> Subject: [meteorite-list] Stones with High Troilite, Low Metal
>
>
> The Rumuruti (R Class) chondrites lack free metal and are sulfide
rich.
>
>
> Laurence
> CMS
> ASU
>
>
> On Jun 26, 2011, at 2:19 PM,
meteorite-list-request at meteoritecentral.com
> wrote:
>
>> Message: 13
>> Date: Sun, 26 Jun 2011 14:55:17 -0400
>> From: Pete Pete <rsvp321 at hotmail.com>
>> Subject: [meteorite-list] Stones with High Troilite, Low Metal
>> To: meteoritelist meteoritelist <meteorite-list at meteoritecentral.com>
>> Message-ID: <BAY153-w48A18A066F0629249C54C5F8540 at phx.gbl>
>> Content-Type: text/plain; charset="iso-8859-1"
>>
>>
>>
>>
>> Sorry about that - once more with a subject:
>>
>>
>>
>> Hi, All,
>>
>> Is there any particular stone meteorite that has a high content of
>
> troilite
> and a low content of free metal?
>>
>>
>>
>> Cheers,
>>
>> Pete
>
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Received on Mon 27 Jun 2011 06:28:50 AM PDT