Rare earth metals are a set of 17 chemical elements which appear in the periodic table and which have similar properties. The unusual name stems from the fact that these metals used to be extracted from minerals (“earths”) which were considered very rare. In reality, however, many of the rare earth metals occur frequently in the Earth’s crust. On the other hand, there are few large deposits containing high concentrations of these elements. The largest occurrences are found in China, particularly in Inner Mongolia. Rare earth metals are used in many key technologies. They are needed for permanent magnets in magnetic resonance imaging (MRI), in the generators of wind turbines and for the production of accumulators, LEDs and plasma screens.