  Magnet.   
Several different rare earths are used, typically in combination with iron, cobalt, or boron, to make very strong magnets. Neodymium-iron-boron magnets are stronger than this samarium-cobalt magnet, but it's still a pretty nice magnet for its size. 
Source: Ed Pegg Jr 
Contributor: Ed Pegg Jr 
Acquired: 20 November, 2002 
Price: Donated 
Size: 0.4" 
Purity: <30%
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