  Silver thermal compound. 
Silver has very good thermal conductivity, so if you're making a paste to aid in heat transfer between a chip and its heat sink, silver seems like a reasonable thing to include in the paste.  No idea how much is actually in this stuff. 
Source: Radio Shack 
Contributor: Theodore Gray 
Acquired: 28 February, 2009 
Text Updated: 1 March, 2009 
Price: $5 
Size: 3" 
Purity: 10%
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