Native Copper, Caledonia Mine.  
This is a heavy lump of naturally occurring copper from the Caledonia Mine, Ontonagon County, Michigan.  Like several of the dozen samples I got from the same source, this one has what look like impressions of pebbles, as it was compressed around them at some point in its history. 
Source: Larry Curtis 
Contributor: Theodore Gray 
Acquired: 10 June, 2003 
Price: $2.50 
Size: 2" 
Composition: Cu
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