Foundry ingot. 
This ingot is one of a bunch I bought from Hall Mark Metals (who also sell on eBay, see source link).  These ingots are intended to be melted down for casting or alloying.  Tin is an absolutely beautiful metal for casting, just a little on the expensive side.  
Source: eBay seller hallmarkmetals 
Contributor: Theodore Gray 
Acquired: 10 April, 2004 
Price: $4.60/pound 
Size: 12" 
Purity: 99.95%
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