[meteorite-list] Nickel free metal in Meteorites

From: Alan Rubin <aerubin_at_meteoritecentral.com>
Date: Fri, 26 Mar 2010 13:12:10 -0700
Message-ID: <73DEFDCEC762454E94C3CB52E52FA1D1_at_SINOITE>

----- Original Message -----
From: <cdtucson at cox.net>
To: "Alan Rubin" <aerubin at ucla.edu>; "meteoritelist"
<meteorite-list at meteoritecentral.com>
Sent: Friday, March 26, 2010 12:23 PM
Subject: Re: [meteorite-list] Nickel free metal in Meteorites


> Alan,
> Wow, I appreciate that your points are put in terms I can follow but Would
> you be so kind as to explain a bit better for me to understand?
> Again, I respect you enough to hear what you are saying but, you lost me
> in some of your points. I will question below in all caps. No, I'm not
> yelling.
> Thanks.
> --
> Carl or Debbie Esparza
> Meteoritemax
>
>
> ---- Alan Rubin <aerubin at ucla.edu> wrote:
>> Low-Ni or Ni-free iron doesn't occur just in some chondrules. It is also
>> found in impact-melt-rock clasts in ordinary chondrites and at the edges
>> of
>> olivine grains in ureilites.
> SO, THIS MAY EXPLAIN THE KALAHARI FIND OF THIS NICKEL FREE IRON? AND YOUR
> INPUT IS HIGHLY APPRECIATED HERE.

                                    I'm afraid I don't know anything about
this.


> These rocks have experienced localized in situ
>> reduction of FeO to metallic Fe as Jeff has pointed out. But let's look
>> at
>> the context, these low-Ni metallic iron grains are situated within mafic
>> silicate grains that have lots of SiO2, MgO and (away from the reduced
>> metal) FeO. They are formed in the solid state. A large iron meteorite
>> isn't situated within a mass of mafic silicate. You could argue that it
>> broke off, but this also wouldn't work. Diffusion of oxygen out of the
>> iron
>> mass would probably take longer than the age of the solar system.
> ARE WE TALKING 13 BILLION YEARS HERE (BIG BANG) ? OR 4.6 BILLION?
> WHY COULD THIS NOT HAVE OCCURRED AT THE TIME OF BIG BANG .THIS WAS VERY
> HOT AND QUICK?

                                I was talking about the age of the solar
system, circa 4.6 billion years. There was no iron at the time of the Big
Bang: only hydrogen, helium and a little lithium. The heavier elements (up
to iron) were forged later in stars by normal fusion processes and did not
enter the interstellar medium until these stars died. Iron and heavier
elements were made in supernova explosions of heavy stars and spewed into
the interstellar medium.




> In
>> addition, iron meteorite falls typically contain at least a few
>> inclusions
>> of troilite, schreibersite, cohenite, graphite, etc. that would not form
>> by
>> reduction of FeO.
> RESPECTFULLY, EXACTLY MY POINT. HOW WOULD WE EVER KNOW IF THESE THINGS ARE
> IN A ROCK THAT WE DISMISS BECAUSE IT HAS NO NICKEL? SEEMS TO ME THERE
> SHOULD BE A BETTER WAY.

                            I have looked at a lot of iron meteorwrongs and
they do not include troilite, schreibersite, and cohenite.


> So, I'm afraid that I don't believe that we're missing
>> real meteorites by categorizing Ni-free iron masses as meteor-wrongs.
> JUST ASKING. I JUST DON'T GET HOW NICKEL IN AN IRON CAN BE 3 TO 60 PERCENT
> AND NOT ZERO PERCENT? ESPECIALLY NOW THAT WE KNOW ZERO PERCENT DOES EXIST
> IN SPACE. SOMETHING DIFFERENT MIGHT BE GOING ON?

                        Metallic Fe can form in two ways. Cosmochemists
surmise that at the beginning of solar-system history there was a hot and
cooling gas of solar composition at low pressure. If we assume a certain
pressure, say 1/10,000 of an atmosphere, the we can calculate the
temperatures at which different elements condense as solids from the gas.
Metallic Ni condenses at 1354 K; metallic Fe condenses at a slightly lower
temperature, i.e., 1337 K. The iron is expected to condense on the Ni grains
to form a solid solution of metallic Fe-Ni. As temperatures drop, these
grains will coarsen. At much lower temperatures, some of the metallic Fe
will react with oxygen and form FeO. This component is generally
incorporated into silicate minerals. A chondrite will generally contain
grains of metallic Fe-Ni and silicates that contain FeO. Except in the most
oxidized chondrites, e.g., R and CK, there is little NiO in the olivine.
So, when we have localized in situ reduction, we can form low-Ni metallic Fe
from the silicates occurring inside the silicate grains. Please note that
volumetrically, the amount of low-Ni metallic Fe is trivial, far less than
0.1% of a typical chondrite. The bulk of the metal grains outside these
silicates will be largely unaffected, except that they may have somewhat
enhanced Fe/Ni ratios at their margins. Bulk melting of these rocks will
merge all of the metal and it will have essentially the cosmic Fe/Ni ratio.
Igneous processes such as fractional crystallization in metallic magmas in
the cores of differentiated asteroids will change the Fe/Ni ratio of
different samples leading to the variety in the irons we see today.



> THANK YOU AGAIN FOR YOUR HELP.
> CARL
>> Alan
>>
>>
>> ----- Original Message -----
>> From: <cdtucson at cox.net>
>> To: "Jeff Grossman" <jgrossman at usgs.gov>; "meteoritelist"
>> <meteorite-list at meteoritecentral.com>
>> Sent: Friday, March 26, 2010 11:06 AM
>> Subject: Re: [meteorite-list] Nickel free metal in Meteorites
>>
>>
>> > Jeff,
>> > Thank you for your well explained points.
>> > As I have said many times before, you would make an excellent teacher
>> > as
>> > your answers always stimulate more thoughts.
>> > On that note. you acknowledge that nickel free metal does exist but,
>> > from
>> > reduced metal and is very small. With all due respect.
>> > Isn't size a relative thing?
>> > I mean looking at things on our scale the size of Nickel free metal in
>> > chondrules is small. So, doesn't this means it could be bigger?
>> > Look no farther than our own planet. We are way different than other
>> > planets.
>> > I have been told by Scientists that the earth is so diverse that it
>> > makes
>> > identification of meteorites difficult. This because Earth can and does
>> > have so many different types of rocks. And this is just one planet.
>> > So, going back to scale. What if this Reducing of Fe O that turns it
>> > into
>> > nickel free iron happens to be really big? Say the scale more like
>> > Artares
>> > which makes Earth look like a grain of sand?
>> > Based on our current method of weeding out meteorwrongs we may never
>> > know
>> > if really big reduction occurs because as part of the weeding process
>> > we
>> > eliminate all metal objects that do not contain nickel. And this
>> > reduction
>> > process as you say is a known fact.
>> > I see more abstracts based on theory than on nickel free iron facts.
>> > Another size scale dilemma is also acknowledged in meteorites. They say
>> > ( tongue in cheek) this is either a very large inclusion and the rest
>> > of
>> > the meteorite is missing. Or this is the whole thing. This is the case
>> > with irons. Sometimes the iron is nearly pure and other times it is
>> > mixed
>> > with silicates as in meso's. But again the point is that these small
>> > bits
>> > of nickel free iron could be big but we will never know.
>> > It seems to me if we paid more attention to morphology and find
>> > location
>> > and less on nickel content (as a must) that we would discover an iron
>> > without nickel. Maybe not as big as Hoba but not as small as what was
>> > found in HAH 237 CBb either. I believe this nickel free iron was also
>> > found in one of the Kalahari Lunar's. Is that from a chondrule also?
>> > This particular meteorite HAH 237 is the one they used recently to
>> > reset
>> > the date of our solar system but not important enough to open our eyes
>> > to
>> > the lack of nickel in bigger meteorites.
>> > I don't get it?
>> > I understand there is always a story. "This thing fell through the
>> > roof"
>> > Okay, does it look man made? Does it have serial numbers on it? Is it
>> > identifiable as an object of any kind like a piece of a tree shredder
>> > blade? If these answers are no then maybe just maybe it did fall from
>> > the
>> > sky? (NJ meteorite).
>> > In this example it was determined to be possible space junk and yet
>> > nobody
>> > bothered to show which space object it could have come from. This
>> > object
>> > would have had a significant amount of not only monetary value but
>> > scientific as well. What was this stainless steel chunk of metal doing
>> > up
>> > in space?
>> > Why would NASA have misplaced such a strange piece of stainless steel?
>> > The
>> > science was dropped but, it came from somewhere. We may never know from
>> > where though. We dropped the ball on NJ and we may be dropping balls
>> > every
>> > day from a lack of nickel. Heaven forbid we find the first large nickel
>> > free iron! Obviously it would be rare but, there are known ungrouped
>> > irons
>> > that are equally rare.
>> > Just another question.
>> > Carl
>> >
>> >
>> > --
>> > Carl or Debbie Esparza
>> > Meteoritemax
>> >
>> >
>> > ---- Jeff Grossman <jgrossman at usgs.gov> wrote:
>> >> 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
>> >> > ______________________________________________
>> >> > Visit the Archives at
>> >> > http://www.meteoritecentral.com/mailing-list-archives.html
>> >> > Meteorite-list mailing list
>> >> > Meteorite-list at meteoritecentral.com
>> >> > http://six.pairlist.net/mailman/listinfo/meteorite-list
>> >> >
>> >> >
>> >>
>> >>
>> >> --
>> >> Dr. Jeffrey N. Grossman phone: (703) 648-6184
>> >> US Geological Survey fax: (703) 648-6383
>> >> 954 National Center
>> >> Reston, VA 20192, USA
>> >>
>> >>
>> >> ______________________________________________
>> >> Visit the Archives at
>> >> http://www.meteoritecentral.com/mailing-list-archives.html
>> >> Meteorite-list mailing list
>> >> Meteorite-list at meteoritecentral.com
>> >> http://six.pairlist.net/mailman/listinfo/meteorite-list
>> > ______________________________________________
>> > Visit the Archives at
>> > http://www.meteoritecentral.com/mailing-list-archives.html
>> > Meteorite-list mailing list
>> > Meteorite-list at meteoritecentral.com
>> > http://six.pairlist.net/mailman/listinfo/meteorite-list
>>
>
Received on Fri 26 Mar 2010 04:12:10 PM PDT