  Anthracite coal.   
I purchased about 1000 pounds in the early 1990s for blacksmithing use by Jim Zimmerman at our farm.  We had to build a special box on the trailer to bring it home, and most of it is still sitting in large plastic containers in the shed.  No problem finding a sample for the table!   
The sound is steel plate being beaten with a blacksmith's hammer after heating in a coal fire. 
Source: Coal Dealer 
Contributor: Theodore Gray 
Acquired: 15 April, 2002 
Price: $0.008/ounce ($250/ton) 
Size: 2" 
Purity: >85%
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