  Carnotite.  
The yellow crust is the carnotite, an ore of uranium that also contains some traces of radium, which is used to justify the name "Radium Ore Revigator" used to describe the water jug you'll find listed under uranium (and which is lined with carnotite). 
Source: eBay seller dr**zarkoff 
Contributor: Theodore Gray 
Acquired: 3 June, 2005 
Price: $15 
Size: 1.5" 
Composition: K2(UO2)2(VO4)2.3H2O
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