|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