Cerium
Cerium is an element that was of value to the Federation. Janus VI was particularly rich in cerium, among many other materials, a fact which was of great interest to the Janus VI colony miners. 

Three months prior to the 's visit in 2267, a new level was opened in the mines, which contained this element and others. It was one of the examples Vanderberg gave to James T. Kirk when explaining their plight. ()

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pt:Cério
Elements