[meteorite-list] Fusion Crust on Irons

[Gary K. Foote]

I have a number of sikhotes that have that nice blue sheen.  Beautiful for sure.  

Gary

On 4 Dec 2006 at 12:10, Dave Freeman mjwy wrote:

> 
> Get a fresh looking blue tinted shikote alin, now that is a fushion crust, about .0008
> thick but still a fine crust of blue steel. Dave F
> 
> Gary K. Foote wrote:
>     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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