Rare Earth Metals
Rare earth metals or rare earth elements are a collection of seventeen chemical elements located at the bottom of the periodic table. They are key elements in the manufacture of high technology components, hybrid cars, etc. Rare earth metals are not radioactive, but rare earth deposits are known to contain thorium, a radioactive element, which makes their mining and refining highly toxic to the environment.
Rare earth metals include: scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, terbium, dysprosium among others. A complete list of rare earth elements can be found here. These metals are not rare in the sense of being scarce, but they are found scattered and in low concentration to be economically exploitable forms.
For more on Rare Earths: