8" mirror. 
This was listed as an IR mirror, but it looks indistinguishable from an ordinary un-etched silicon semiconductor wafer.  Probably is, just repackaged for use as a mirror. 
Source: eBay seller terri63097 
Contributor: Theodore Gray 
Acquired: 15 October, 2004 
Price: $15 
Size: 8" 
Purity: 99.9999%
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