Molybdenum mirror. 
I have no idea what these things are for, but they seem to be associated with some kind of laser application.  They are tiny, less than 1/4" long overall.  The box says they are 1/4 wave mirrors, which means the surface is certified to be flat to within 1/4 of the wavelength of the light they are intended to be used with, about 10 microns in the deep infrared. 
A claim I find to be somewhat dubious.  I mean, just look at the things: Do they look like mirrors to you?  Any part of them?  If you know anything about these devices, I'd like to hear about it. 
Source: eBay seller vanagon 
Contributor: Theodore Gray 
Acquired: 1 August, 2003 
Price: $10 
Size: 0.20" 
Purity: 99%
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