[meteorite-list] Nickel free metal in Meteorites

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Thu, 25 Mar 2010 18:32:04 -0400
Message-ID: <4BABE464.6010808_at_usgs.gov>

Ni-free metal occurs within chondrules that have experienced reduction
during melting. These chondrules were originally mostly free of metal
and therefore free of Ni, but contained oxidized iron (FeO) in the
silicate minerals. During reduction, the FeO was converted into Fe
metal (if the reducing agent was H2, then you'd also make H2O; if it was
C then you'd make CO/CO2). The pure Fe metal that is made can manifest
itself as "dusty metal" grains within olivine crystals, or sometimes can
coalesce into larger Fe metal particles in the chondrule.

The thing about this is, it is a local effect within a few chondrules.
Most of the metal in the chondrite is still Ni-bearing. There is no
easy way to make large masses of this pure Fe metal, such as would form
iron meteorites, because any process that would segregate metal, would
segregate all of it, not just these strange particles.

Jeff

On 2010-03-25 5:59 PM, cdtucson at cox.net wrote:
> List,
> During recent research into CBb chondrites I stumbled upon an article from 2007 with references from Rubin that shows an image of a CC chondrite with nickel free metal.
> How is this possible?
> In past conversations with Scientists when I have asked why do iron meteorites always have to have nickel. The typical response is that they not only have to have nickel but, it has to have a few percent of nickel and not just PPM's of it. In explanation of this as I recall, I've always been told the reason that meteoritic iron always has to have Nickel is because in nature there is no way to separate the two elements.
> If that is true then how is it that in this case we do in fact have meteoritic metal without nickel? somehow they got separated.
> Unless this analysis is wrong does this not teach us that yes in fact there can and does exist meteoritic iron devoid of nickel. And therefore there not only could be Iron meteorites without nickel but,this ups the odds that there in fact are meteorites without nickel.
> Please see attached abstract. Back scattered images Figure 2 at the fifth page from the top of the article. It says;
> "D. Close up of a CC Chondrule texture. Radiating unidentified minerals and Nickel free metal (met) are set up in a silica-rich matrix."
>
> http://www2.mnhn.fr/hdt205/leme/doc/2007%20Gounelle%20et%20al.%20EPSL.pdf
>
> Thanks Carl
>
> --
> Carl or Debbie Esparza
> Meteoritemax
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-- 
Dr. Jeffrey N. Grossman       phone: (703) 648-6184
US Geological Survey          fax:   (703) 648-6383
954 National Center
Reston, VA 20192, USA

Received on Thu 25 Mar 2010 06:32:04 PM PDT