  Japanese coin. 
I know I brought back a handful of these last time I was in Japan, but I can't find any of them.  Fortunately Ed had some, and it's not like they're actually worth anything, which is why they are made of aluminum in the first place.  Reader Lawrence Spiwak told me an interesting fact: A one yen coin is exactly two cm in diameter, and weighs exactly one gram.  I've verified this to 5 decimal places with my analytic balance, so I know it's true. 
Source: Japan 
Contributor: Ed Pegg Jr 
Acquired: 6 September, 2002 
Text Updated: 9 April, 2009 
Price: Donated 
Size: 0.5" 
Purity: >90% 
Sample Group: Coins
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