Aluminum Penny. 
This is an incredibly rare coin: An experimental penny made to see if aluminum would be a good substitute for copper, when the price of copper rose to more than a penny per penny.  Only a very small number were every minted, because they decided to go with copper-clad zinc instead.  In fact, the coin is so rare that I couldn't possibly actually have one: This is a copy made by a company that specializes in making (legitimate) copies of extremely rare coins.  Note that it's clearly stamped "COPY" so there is no confusion. 
Source: eBay seller dlrguy 
Contributor: Theodore Gray 
Acquired: 11 July, 2003 
Price: $10 
Size: 1/2" 
Purity: >99% 
Sample Group: Coins
 |  
  |  
 |  
  |