Promethium Discovered in 1947, Promethium is the only rare-earth that has never been found in nature. This makes this element the least abundant in the earth's crust because there is absolutely none.
Promethium belongs to the lanthanide series .
Promethium-147 is used in luminescent coatings for instrument dials and as a power source for semiconductor solar batteries for space use. It is also used as a source of X-rays for medical applications in areas of the world where electrical power is not generally available. Shown above is an oxide of promethium.