[meteorite-list] R Chondrites and Magnetism

[MexicoDoug at aol.com]

Bernd, as you rectify Tom's synthesis of  everything thus far, to "*Some* 
R-chondrites have *j u s t* enough metal to be  attracted to a strong enough 
magnet" - that's not what you meant to say, I  cannot help believing.  I had 
posted (and you also later cited) the  literature the paper describing the 
magnetism to the pyrrhotite which is about  5% of the weight percent of the material 
at least in the type specimen.   You even quoted O. Richard Norton's book, 
which I will will also do, page  191:  "The pyrrhotite is magnetic giving the 
meteorites weak magnetic  attraction."  The rest of Norton's comments and yours 
supports that there  is little or no reduced metal:

See once again, Meteoritics V. 29, No. 2,  pp. 275-286 March 1994
"Mineralogy and Chemistry of Rumuruti: The First  Meteorite Fall of the New R 
Chondrite Group" by Schulze, H.; Bischoff, A.;  Palme, H.; Spettel, B.; 
Dreibus, G.; Otto, J.

It is clear to me that with  a strong enough magnet whatever that means funny 
things can happen, but I think  you were more focussed on why the rock is 
attracted to a magnet in the  listmember type tests (indeed why it is a magnet, 
too).  This  is due  according to the literature the pyrrhotite as best as I 
can tell, which I  wouldn't call metal, but just a magnetic mineral, causing the 
debil magnetism of  the rock as a whole.

Thus, careful, as the literature does support the  high oxidation levels, but 
it does not support that the magnetism some list  members are observing as 
being due to *j u s t* enough metal, but rather  principally to the low content 
of the magnetic pyrrhotite mineral, which is iron  "oxidized" by an excess of 
sulfur under oxidizing conditions.  Recal that  pyrrhotite is magnetic but 
troilite isn't, and troilite is stochiometric FeS -  i.e., when an equal or 
excess of iron is present, and not the oxidative  reverse.  Of course you may have 
another source backing up the magnetic  metal grains (which are in the trace 
level per 1994 paper)?  If I have  missed something, it would be nice to know 
your thinking!  How much  susceptibiulity the hypothetical free metal 
contributes seems to be another  question with no support nor quick and dirty magnet 
test.  I did notice  that you added "some" which could mean one, but I don't get 
that that was your  thinking, either...

And errrr... what's this about water in space  ;-)
Saludos, Doug


En un mensaje con fecha 05/31/2005 2:01:22 PM  Mexico Daylight Time, 
peregrineflier at npgcable.com escribe:
"extensive aqueous  alteration on the R parent body"

Water in space? That sounds like a whole  new subject! : ) 

Good grief, Tom


Thanks,  Tom
peregrineflier <><

----- Original Message ----- 
From:  <bernd.pauli at paulinet.de>
To:  <Meteorite-list at meteoritecentral.com>
Sent: Tuesday, May 31, 2005 11:48  AM
Subject: [meteorite-list] R Chondrites and Magnetism


> Tom  concluded:
> 
> > So, most R's have enough metal to be
>  > attracted to a powerful enough magnet
> 
> Careful, please. I'd  like to add the little word "just",
> leave out the word "most" and  replace it by "some":
> 
> > Some R's have  j u s t   enough metal to be
> > attracted to a powerful enough magnet  ...
> 
> This sounds better because almost all the iron is oxidized  and
> also FeNi (nickel-iron) is extremely rare (only some tens of  parts
> per million!)
> 
> In his Cambridge Encyclopedia, O.R.  Norton writes on p. 116:
> 
> "There is almost no free iron metal (a  few grains here and there) ..."
> 
> > ... if I can find out why  R's have so little metal.
> 
> Oxidation (water was the oxidizing  agent):
> 
> Step 1: extensive aqueous alteration on the R parent  body
> Step 2: dehydration (removal of water) + thermal  metamorphism
> 
> 
> Best wishes,
> 
>  Bernd
> 
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