  Old photographic flash bulb. 
Back in the dark ages, cameras used one-time-only flash bulbs that ignited a fine wire inside a glass bulb.  We're not concerned here with the fine wire, but rather with the "igniter": these top-quality GE #5 bulbs were advertised as coming with "the guaranteed RHENIUM igniter".  I don't know for sure what metal the wire in this one is made of, but I have a different type under zirconium which is labeled as using a wire of that metal (but that one doesn't say what it's igniter is made of). 
Reports Tryggvi: 
The woolly stuff in GE flashbulbs is zirconium. (I.e. , the stuff that burns and makes the light. The bulbs are also filled with a few atmospheres of oxygen). The flashbulbs in the cubes that were used on some Kodak Instamatics were not triggered electrically (with rhenium wire), but with a percussive pyrotechnic mix inside a little metallic tube that stuck out of the bulb.  
Source: eBay seller erinsplace 
Contributor: Theodore Gray 
Acquired: 1 August, 2002 
Text Updated: 29 January, 2009 
Price: $1 
Size: 1.5" 
Purity: >50%
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