One company exploits this phenomenon by making nanoparticles of the compound cerium oxide, which in that form are chemically reactive enough to serve as a catalyst.
Prices have soared: the cost of cerium oxide (often used as a catalyst) has increased sixfold since the start of the year, and is 20 times higher than in 2005.
Exactly what is a rare earth metal is very slightly arguable, some would say it is only the lanthanides, lanthanum, cerium through to lutetium in that little box at the bottom of the periodic table.