[meteorite-list] Silicated Iron vs. Winonaite

From: Jason Utas <meteoritekid_at_meteoritecentral.com>
Date: Mon, 29 Mar 2010 00:12:29 -0700
Message-ID: <93aaac891003290012u210d94b7v252512180352bb79_at_mail.gmail.com>

Hello Jeff, All,
An excellent point - it's hardly a question since your hypotheses were
spot-on.
All of these paired "metal-rich winonaites" are actually *the same
meteorite* as the silicated iron NWA 2680.

http://www.encyclopedia-of-meteorites.com/meteorite.aspx?id=33173

http://www.encyclopedia-of-meteorites.com/meteorite.aspx?id=34296

Generally speaking, I believe the difference in classifications lies
in the quantity of iron versus silicate material - a hard distinction
to make when many silicated irons are heterogeneous, and an
ill-defined border anyways (at least one that isn't addressed in any
literature I know of).

But..one is an iron meteorite with silicate inclusions, and the other
is a meteorite composed primarily of silicates, as per the traditional
groups.

That said, I've been more than a little annoyed with all of these
"metal-rich winonaites" that are clearly paired to 2680.
Maybe the labs got/were sent particularly silicate-rich samples, or
maybe they're just not accustomed to dealing with iron meteorites --
or maybe some dealers figure that a "winonaite can bring in more $$
than a "silicated iron."

Whatever the case, calling these things "metal-rich winonaites" when
they're really just pieces of an iron (albeit a truly beautiful one)
with a large number of fairly typical silicate inclusions, seems wrong
to me. The vast majority of samples are >60-70+ percent iron, and
that iron is characteristic of iron meteorites.
Sounds like a silicated iron to me.

I just realized something else -- the classificaiton "metal-rich
winonaite" tells you two things. It's a winonaite, and it's got a lot
of metal. The classification "IAB with winonaite inclusions" tell you
significantly more about the meteorite. It tells you the composition
of the iron as well as the composition of the silicates.
I would personally choose the more informative classification; even if
it's just as "accurate," it's more useful to boot.

Regards,
Jason

On Sun, Mar 28, 2010 at 11:37 PM, Jeff Kuyken <info at meteorites.com.au> wrote:
> G'day List,
>
> I have a question I'm hoping someone may be able to answer as I don't know
> if I have this right. My (basic) understanding is that the silicate parts of
> a silicated iron are actually Winonaite material. When this silicate
> material is found without iron, then they are classified as a Winonaite but
> with/in an iron then they become a silicated iron.
>
> Is this right or am I way off here? There seem to be an increasing amount of
> silicated irons being classified as a Winonaite. So when is a silicated iron
> not a Winonaite and vice-versa?
>
> Thanks,
>
> Jeff
>
>
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Received on Mon 29 Mar 2010 03:12:29 AM PDT