Rare earth elements and rare earth metals are, according to IUPAC, the collection of seventeen chemical elements in the periodic table, namely scandium, yttrium, and the fifteen lanthanoids. The former two are included as they tend to occur with the latter in the same ore deposits.
Rare earth elements became known to the world with the discovery of the the black mineral ytterbite (also known as gadolinite) by Lieutenant Karl Arrhenius in the year 1787, in a quarry in the village of Ytterby, Sweden. Many of the rare earths are named in honor of the scientists who discovered or elucidated the elemental properties, geographical discovery, Latin or Greek, or mythology:
| Lanthanum | from the Greek "lanthanon" meaning I am hidden. |
| Cerium | after Greek deity of fertility, Ceres. |
| Praseodymium | from the Greek "praso" which means leek-green. |
| Neodymium | from a Greek word "neo" which means new-one. |
| Promethium | after Prometheus who brought fire to mortals. |
| Samarium | Vasili Samarsky-Bykhovets discovered the rare-earth ore called samarskite. |
| Gadolinium | after Johan Gadolin (1760-1852) to honor his investigation of rare earths. |
| Dysprosium | from the Greek "dysprositos" meaning hard to get. |
| Thulium | refers to the mythological land of Thule. |
| Ytterbium | named after the Ytterby, Sweden, where the first rare earth ore was discovered. |
"Earth" is an obsolete term for oxide; it is a translation from the French terre as French was the lingua franca when these elements were discovered at the beginning of the 19th century. "Rare" was used because some of these elements were believed to be scarce in abundance as minerals. However, these elements are in fact, except the highly-unstable promethium, relatively abundant in the Earth's crust; the most abundant, cerium, at 68 parts per million, is the 25th most abundant element in the crust, more common than lead, while even the least abundant "rare" earth element, lutetium, is 200 times more abundant than gold.
The principal economic sources of rare earth elements are the rare-earth minerals bastnasite, monazite, and loparite and the lateritic ion-adsorption clays. Despite their relative abundance, however, these are more difficult to mine and extract than the sources of transition metals (due in part to their very similar chemical properties), making them relatively expensive. Their industrial use was very limited until efficient separation techniques were developed, such as ion exchange, fractional crystallization and liquid-liquid extraction during the late 50's and early 60's.
The following abbreviations are often used:
For more details of the properties and uses of these elements, refer to the lanthanoids article.
