Re: Elemental abundances on Earth

From: Mike Dworetsky (platinum198_at_pants.btinternet.com)
Date: 11/26/04 

Date: Fri, 26 Nov 2004 17:15:08 +0000 (UTC)

"Michael Mcneil" <weatherlawyer@hotmail.com> wrote in message
news:79e4d902cea719f0268989b8a2560333.45219@mygate.mailgate.org...
> "Mike Dworetsky" <platinum198@pants.btinternet.com> wrote in message
> news:cnnl7l$kpq$1@hercules.btinternet.com
>
> > Only a tiny amount of metallic iron comes from meteorites. This
> > stuff is so rare that in some remote cultures the only source of iron
was a
> > meteorite,
>
> I thought the first poster was a nit until I read yours. I am sure
> you can see the error in your reply.
>
> You don't happen to work for Earth Observatory by any chance?
>

Sorry, I don't quite follow what you are trying to imply, though I suspect
an insult is involved. "This stuff" referred to meteoric iron. Terrestrial
iron ultimately originates from iron contained in the original cloud that
condensed into the solar system and planets. Only in that sense is most
iron on Earth meteoritic. A later reply from the OP says that, in effect,
what his friend was claiming is that modern iron ore bodies such as Mesabi
Range in the US and the Western Australian deposits are meteoritic, but they
are not, they are sedimentary:

>From the Mineral Information Institute web site:

"Hematite is iron oxide (Fe2O3). The amount of hematite needed in any
deposit to make it profitable to mine must be in the tens of millions of
tons. Hematite deposits are mostly sedimentary in origin, such as the banded
iron formations (BIFs). BIFs consist of alternating layers of chert (a
variety of the mineral quartz), hematite and magnetite. They are found
throughout the world and are the most important iron ore in the world today.
Their formation is not fully understood, though it is known that they formed
by the chemical precipitation of iron from shallow seas about 1.8-1.6
billion years ago, during the Proterozoic Eon."

I stand by my statement that many "primitive" cultures derived most of their
iron from rare meteorite falls (for example the Inuit).

The Earth's crust is about 5% iron, mostly in the form of oxides and other
minerals. This iron is not meteoritic except in the most general
(first-cause) terms as I have outlined. It exists as rich exploitable
deposits only because of various chemical reactions and sedimentation over
the Earth's geological past.

Who or what is Earth Observatory? I don't work for them. 

-- 
Mike Dworetsky
(Remove "pants" spamblock to send e-mail)

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