Boron Nitride ceramic disk. 
This ceramic-like disk came from a scrap yard and was claimed to be or contain boron.  I don't think it's pure boron, but it could well be a boron nitride ceramic.  Unfortunately the analytical instruments available to me don't work on low atomic number elements, so I have no good way of testing what it really is. 
Source: John Wechselberger 
Contributor: John Wechselberger 
Acquired: 15 April, 2004 
Price: Donated 
Size: 4.5" 
Purity: <50%
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