[meteorite-list] a question on fusion crust

[Michael Murray]

Hi List,
Are you ready for a dumb question!  Here goes...  Is there a more  
definitive description of the blackened outer layer on the surface of  
iron meteorites than simply referring to it as "fusion crust"?  From  
what I can gather looking at different pictures of stonys, they seem  
to have a glassy or melted layer of the material of the stone.  I can  
see that being a 'crust'.  On at least some irons, there is a coating  
but it doesn't appear glassy, just blackened.   I'm guessing that  
that coating is partially resulting from burning of the gases in the  
atmosphere?  If it is a 'crust', it is not much of one.  It looks  
like a very thin coating of soot that is adhered to the stone,  
although more durable than soot.  This is probably one of those dumb  
questions that the Collection of Wisdom would answer.

The stone in this picture has the blackened layer I'm referring to:

<http://i127.photobucket.com/albums/p124/mmurray_02/IMG_0319.jpg>

Michael Murray