Rare Earth Elements: Critical Resources for High Technology

This is the United States Geological Survey's own Fact Sheet 087-02, Rare Earth Elements, Critical Resources for High Technology, published in 2002 by Gordon Haxel, James Hedrick and Greta Orris. As a government scientific agency's own reference document it is authoritative for the basic geology and industrial use of the rare earth elements it describes. Its limit, worth naming directly, is that the fact sheet itself is internally inconsistent on one point: page two names thulium and lutetium together as the two least abundant rare earth elements without ranking them, while page four separately calls lutetium the least abundant. A single authoritative document disagreeing with itself across its own pages is the clearest evidence available that the precise ranking is not a settled fact, and a claim citing this source for that ranking should say so rather than pick one page silently.