[meteorite-list] Fusion Crust on Irons

[Gary K. Foote]

Thanks for clearing that up Doug.  I've always felt a bit dumb talking about fusion crust 
and irons.

Gary

On 4 Dec 2006 at 13:59, MexicoDoug wrote:

> 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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>