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Re: Widmanstatten pattern question
On Fri, 3 Jul 1998 09:31:09 -0400 Bob King wrote:
> From: Bob King
> Date: Fri, 3 Jul 1998 09:31:09 -0400
> Subject: Widmanstatten pattern question
> To: meteorite-list@meteoritecentral.com
>
> Hello all,
>
> I recently etched several iron meteorites including a peculiar twisted hunk of
> metal I suspected to be a meteorite. After etching this last piece a pattern that
> could be the Widmanstatten Pattern was visible but it looked different from
> Canyon Diablo and Odessa. Therefore I'm not sure if what I have is an artifact or
> a real iron meteorite. Since I'm not an expert on Widmanstatten patterns I
> wonder if someone on this list might be able to tell me whether etching an iron
> (manmade) artifact produces any pattern at all. If not then perhaps I do have a
> meteorite. In the meantime I'm going to polish another surface, etch it and see
> what comes up.
> Thanks for any help you might be able to offer!
>
> Bob King
>
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Hello Bob!
I am a novice to the field, but...
As far as I know man made objects could make a pattern when etched.
An example would be a sword from Japan. The edge of these swords
have been tempered so the steel is harder there then anywhere else
on the sword. Sometimes if the sword is not polished you can't really
tell if there is a tempered "design"- "hamon", but with the use of an acid
like ordinary lemon juse the hamon, if any becomes apparent.
Going back to meteorites. A widmanstatten pattern is not the only one
possible, and also there are diffrent kinds of widmanstatten pattern
This depends on the angle to the cristal lattuce the meteorite had been
cut. In octahedrites the nickel-iron alloy is 7%-13% nickel and when
etched displays intergrowth of taenite (light in colour,nickel-iron alloy
with at least 20% nickel) and kamacite (dark, not more than 7.5% nickel).
If cut at 90 degrees to the crystal luttice the pattern displayed will look
like the most popular widmanstatten one with interlocking kamacite and
taenite. If cut at 60 or 120 degrees the pattern will have a kind of "triangle"
look, that is will no longer have the up and down fabric like structure.
If it is cut at random it will have a blotchy look. This could be compared to
using water colours and making colour splats that have oval edges (Odessa).
In hexahedrites which are 4.5% to 6.5% nickel the etched pattern is called
Neumann lines. These lines are parallel running along the plane of the crystal.
In ataxites the bands disappear and the meteorite becomes "structureless"
(13% nickel, less then 16%) ex. Santa Catharine, Brazil
As to Canyon Diablo I only could find a picture of it where the line pattern
was made by a saw, and the only thing that I know about these irons is that they
are carbon rich therefore I could not comment on the structure.
I hope I didn't insult you with all this info that you probably knew, but this
is the only help I could offer.
If you could provide a photo I could ask some friends at the University of
Toronto. I don't think that without an analysis of the mineral composition
you could get a definite answer. I'm sure that somebody else on the list
(with more experience) could be of more help.
And hopefully they will take the time to reply to you.
Brest regards,
Kasia
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