RARE EARTH ELEMENT

'Rare earth elements' and 'rare earth metals' are a collection of sixteen chemical elements in the periodic table, namely scandium, yttrium, and fourteen of the fifteen lanthanides (excluding promethium), which naturally occur on the Earth. The former two are included as they tend to occur with the latter in the same ore deposits. Some definitions additionally include the actinides. The terms "rare earth" and "rare earth metal" are trivial names that fall outside the official IUPAC nomenclature system. Outside of a strict scientific context, however, the terms retain their usability; for instance, the United States Patent and Trademark Office (USPTO) includes the term "rare earth" in the classification of metal alloys and other compounds, as well as distinguishing rare-earth magnets from other types of magnet.
Rare earth elements became known to the world with the discovery of the the black mineral ytterbite (alternately know as gadolinite) by Lieutenant Karl Arrhenius in the year 1887, in a quarry in the village of Ytterby, Sweden. ^[1] Many of the rare earths are named in honor of the scientists who discovered or ellucidated the elemental properties, geographical discovery, Latin or Greek, or mythology:

Gadolinium	Johan Gadolin (1760-1852), to honor his investigation of rare earths.
Samarium	V.E. Samarsky, discovered the rare-earth ore called samarskite.
Ytterbium	named after the Ytterby, Sweden, where the first rare earth ore was discovered.
Thulium	refers to the mythological land of Thule.
Promethium	after Prometheus who brought fire to mankind.
Cerium	after Greek deity of fertility, Ceres.
Lanthanum	from the Greek lanthano meaing I am hidden.
Dysprosium	from the Greek dysprosodos meaing troublesome accessibility.
Praseodymium	from the Greek parson which mean leek-green.
Neodymium	from a Greek word which means new-one.

"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, the term "rare earth" is now deprecated by IUPAC, as these elements are (except highly-unstable promethium), in fact 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 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 effecient separation techniques were developved, such as ion exchange, fractional crystalization and liquid-liquid extraction durring the late 50's and early 60's. ^[2]
The following abbreviations are often used:

★ REE = rare earth elements

★ LREE = light rare earth elements (La-Sm)

★ HREE = heavy rare earth elements (Eu-Lu)
For more details of the properties and uses of these elements, refer to the lanthanides article.

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References

References

1. 1787-1987 Two hundred Years of Rare Earths, , , , Rare Earth Informaiton Center, IPRT, North-Holland, 1987
2. Spedding F, Daane AH: "The Rare Earths", John Wiley & Sons, Inc., 1961