  Pressed sputtering target. 
Look back a few samples and you'll see a slice of the outer rim of a disk like this.  After seeing how beautiful the surface of that slice was, I could not pass up the opportunity to have a full disk of the stuff.  Normally these disks would have their irregular outer rim cut off (resulting in samples like he previous rind), but this one ended up slightly under-sized, making it a reject. 
 
Along with the full disk came an explanation from the source of how the disks are made.  Basically they start with a tall cylinder and squash it at low temperatures (-50C) and tremendous pressure (1600 tons).  The surface texture is a result of large crystal grains in the material sliding against each other. 
 
You can read all about the process in the the patent that covers it. 
  
Source: eBay seller mrj33 
Contributor: Theodore Gray 
Acquired: 2 February, 2008 
Text Updated: 23 February, 2008 
Price: Anonymous 
Size: 13" 
Purity: 99.9996%
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