Four and a half pound lump. 
This is a really great rock of silicon.  I don't know the purity, but this is probably one of the intermediate stages in the purification of silicon from sand to boule, so I'm guessing it's around 5-nines, but this is just a guess.  What I do know for sure is that it's a wonderful thing to hold, with the typical shiny metallic-yet-not-metal surface of silicon.  The next stage in purification is the rod pictured above, and the step before this one is the lump pictured below. 
Source: eBay seller gardnrobe 
Contributor: Theodore Gray 
Acquired: 11 July, 2003 
Price: $31 
Size: 8" 
Purity: >99.999%
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