Extracted from another site:

What are the rare earth elements and how are they used?

First discovered in the 18th century, the rare earth metals were long considered chemical curiosities rather than the vital building blocks fortechnology.

After their discovery by a Swedish scientist in 1787, a total of 17 of the soft metals were identified. Despite their name, they are relatively abundant in the Earth's crust but the high cost of extraction means only areas with rich deposits are worth exploiting.

The arrival of new technology means that global production has risen from less than 5,000 tonnes in 1955 to the current level of about 120,000 tonnes a year.

*Cerium (Ce) – catalytic converters for diesel engines

*Praseodymium (Pr) – an alloying agent for aircraft engines

*Neodymium (Nd) – a key component of high-efficiency magnets and hard discdrives

*Lanthanum (La) – a major ingredient for hybrid car batteries

*Samarium (Sm) – lasers and nuclear reactor safety

*Promethium (Pm) – portable X-rays and a nuclear battery

*Gadolinium (Gd) – shielding for nuclear reactors, compact discs

*Dysprosium (Dy) – improves the efficiency of hybrid vehicle motors

*Terbium (Tb) – a component in low-energy light bulbs

*Erbium (Er) – fibre optics

*Europium (Eu) – used in flat screen displays and lasers

*Holmium (Ho) – nuclear control rods, ultra-powerful magnets

*Thulium (Tm) – lasers, portable X-rays

*Ytterbium (Yb) – monitoring equipment for earthquakes

*Lutetium (Lu) – oil refining

Two more elements, Scandium and Yttrium, are considered rare earths as theytend to occur in the same ore deposits and have similar chemical properties.