[meteorite-list] Franconia area chondrites and Irons

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Sun Jul 25 21:49:12 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C86904EE5E83_at_US-Torrance.mail.saic.com>

Hi Ruben and List,

Wanted to add some info on the irons from the Franconia area:

> The tiny irons we've found have not yet been seriously
> considered as being related to the Dutch Flat Iron. This
> is partly because a lot of time has NOT been devoted to
> studying them. Also as I recall the Dutch Flat iron is a
> coarse or coarsest octahedrite and displays a wide
> Widmanstatten pattern.

Dutch Flat actually does NOT display a typical Widmanstatten pattern,
which is what initially led me to believe it was a hexahedrite. (The
pattern looks more like Neumann lines). However, Dutch Flat is a
low-Iridium coarsest octahedrite; its size (< 50 grams) was too small
to show the kamacite/taenite boundaries.

> The one Franconia iron I tried to etch seemed to have no
> recognizable pattern at all, instead it was very grainy. (Keep
> in mind the iron I attempted to etch did have a high percentage
> of nickel, least anyone think it was not a meteorite).

This would be completely consistent with a pairing to Dutch Flat,
so you can understand my interest in getting it analyzed.

> However, When I etched a Franconia chondrite with large metal
> veins a very brilliant medium to fine widmanstatten pattern did
> appear. What does all this mean? I don't know but more help is
> on the way.

It says that the Franconia area irons are almost certainly unrelated
to the H5 chondrites, and that a very good chance remains that those
irons are paired to Dutch Flat. No one here needs to be told that
iron meteorite finds are much rarer than stony meteorites; so, the
notion that *two* unpaired iron meteorite finds would be made within
a few miles of each other seems far less likely than the simpler
alternative that they are paired, particularly when neither shows
a fine- or medium octahedrite W-pattern.

Best,
Rob
Received on Sun 25 Jul 2004 09:39:00 PM PDT