[meteorite-list] Fusion Crust on Irons

[MexicoDoug]

Hi Gary,

Fusion crust can be in the eyes of the beholder, so the difficulty with this 
question is we are making a one-size fits all definition.

For the irons, you could get a verrrry thin local destruction of any 
crystalline patterns or figures (no longer etch), some chemical change from 
'burning' up including colors.  In the case of stones, it is a different and 
typically a glazed-silicate ceramic crust forms.  It can get a rainbowish 
tint from burnishing, though it usually looks somewhat bluish.  It's so thin 
that it quickly is lost to other mineralization in the oxidizing humid 
environment that is earth's.

So there is a difference.  But loosely thay can all be attributed to 
'fusion' though in the case of iron it has a different characteristic.  In 
either case, when the fusion crust is black, this is generally caused by 
oxidized iron during the entry, not terrestrialization. That is a main 
difference between what we see on many older irons in dry and stable 
environments.

So, yes, irons can have a fusion crust, it is just not predominantly a 
ceramic kiln glaze best seen from some achondrites, which is the classic...

Best wishes, Doug


----- Original Message ----- 
From: "Gary K. Foote" <gary at webbers.com>
To: <Meteorite-list at meteoritecentral.com>
Sent: Monday, December 04, 2006 1:26 PM
Subject: [meteorite-list] Fusion Crust on Irons


> Hi All,
>
> Recently I have read a few posts to this list that definitively claim that
> irons do not form a fusion crust.  Yet, in Norton's "Rocks From Space",
> [pg 167 in my softbound edition] it clearly states the following;
>
> "Iron meteorites have the thinnest crust of all, usually only a small
> fraction of a millimeter thick.  A fresh crust is blue-black to black and
> looks like freshly welded steel.  This crust is fragile and easily
> destroyed if the meteorite weathers for even a short time."
>
> So, which is true?  Crust or no crust for irons?
>
> Gary Foote
> http://www.meteorite-dealers.com
>
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