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Comments on celestial iron

I wanted to mention a few technical things about meteorite
structures and etching.

First the crystalline structures that are exhibited after etching
are called Widmanstatten structures.

Ni-Fe meteorites are composed of two primary phases of Ni-Fe alloy;
they have different cooling/crystallization rates and are
fractionally crystallized. (Terrestrial alloys will exhibit similar
structures when etched).

Each distinct meteorite fall exhibits a unique Widmanstatten
pattern. (This should not be a surprise as they are each chemical
distinct and undergo a unique set of physical influences when they
hit the atmosphere, lots of variables. All affecting the ultimate
structures exhibited when etched, that =92s why the =93pros=94 can loo=
k at
a slice and tell you it=92s a Gibeon or a Canyon Diablo.

There a re a number of methods used for etching meteorites, most are
dangerous to ridiculously so. The one I have used calls for a hot
mix of nitric and alcohol, it works very well and is very dangerous,
the vapors are extremely volatile and mobile. The last time I used
this solution I was outside with a fan blowing across the work
surface wearing shoulder length rubber gloves, a rubber apron and a
full face respirator and still the fumes managed to get underneath my
chin and stay there long enough to burn me.

This problem would not have occurred had I been using a fume hood. I
don=92t know many dealers who have those as part of their arsenals.
Use caution when etching; refer to a number of the online sites that
address the procedures.

Christopher L. Johnston
PO Box 354
Fax ++264-64-57-0548
Omaruru ~ Namibia