I am curious too, so I made some research and end up with these from mnn –
mother nature network.
"Rare earth" metals aren't as rare as they sound — in fact, you're probably using some right now. They're key to a variety of everyday devices, from tablet computers and TVs to hybrid cars and wind turbines, so it may be encouraging to know several kinds are actually common. Cerium, for example, is the 25th most abundant element on Earth.
So why are they called "rare" earths? The name alludes to their elusive nature, since the 17 elements rarely exist in pure form. Instead, they mix diffusely with other minerals underground, making them costly to extract.
And, unfortunately, that isn't their only drawback. Mining and refining rare earths makes an environmental mess, leading most countries to neglect their own reserves, even as demand soars. China has been the main exception since the early 1990s, dominating global trade with its willingness to intensively mine rare earths — and to deal with their acidic, radioactive byproducts. That's why the U.S., despite large deposits of its own, still gets 92 percent of its rare earths from China.
Rare earths roster
Here's a closer look at some of the ways each rare earth element is used:
Scandium: Added to mercury vapor lamps to make their light look more like sunlight. Also used in certain types of athletic equipment — including aluminum baseball bats, bicycle frames and lacrosse sticks — as well as fuel cells.Yttrium: Produces color in many TV picture tubes. Also conducts microwaves and acoustic energy, simulates diamond gemstones, and strengthens ceramics, glass, aluminum alloys and magnesium alloys, among other uses.
Lanthanum: One of several rare earths used to make carbon arc lamps, which the film and TV industry use for studio and projector lights. Also found in batteries, cigarette-lighter flints and specialized types of glass, like camera lenses.
Cerium: The most widespread of all rare earth metals. Used in catalytic converters and diesel fuels to reduce vehicles' carbon monoxide emissions. Also used in carbon arc lights, lighter flints, glass polishers and self-cleaning ovens.
Praseodymium: Primarily used as an alloying agent with magnesium to make high-strength metals for aircraft engines. Also may be used as a signal amplifier in fiber-optic cables, and to create the hard glass of welder's goggles.
Neodymium: Mainly used to make powerful neodymium magnets for computer hard disks, wind turbines, hybrid cars, earbud headphones and microphones. Also used to color glass and to make lighter flints and welder's goggles.
Promethium: Does not occur naturally on Earth; must be artificially produced via uranium fission. Added to some kinds of luminous paint and nuclear-powered microbatteries, with potential use in portable X-ray devices.
Samarium: Mixed with cobalt to create a permanent magnet with the highest demagnetization resistance of any known material. Crucial for building "smart" missiles; also used in carbon arc lamps, lighter flints and some types of glass.
Europium: The most reactive of all rare earth metals. Used for decades as a red phosphor in TV sets — and more recently in computer monitors, fluorescent lamps and some types of lasers — but otherwise has few commercial applications.
Gadolinium: Used in some control rods at nuclear power plants. Also used in medical applications such as magnetic resonance imaging (MRI), and industrially to improve the workability of iron, chromium and various other metals.
Terbium: Used in some solid-state technology, from advanced sonar systems to small electronic sensors, as well as fuel cells designed to operate at high temperatures. Also produces laser light and green phosphors in TV tubes.
Dysprosium: Used in some control rods at nuclear power plants. Also used in certain kinds of lasers, high-intensity lighting, and to raise the coercivity of high-powered permanent magnets, such as those found in hybrid vehicles.
Holmium: Has the highest magnetic strength of any known element, making it useful in industrial magnets as well as some nuclear control rods. Also used in solid-state lasers and to help color cubic zirconia and certain types of glass.
Erbium: Used as a photographic filter and as a signal amplifier (aka "doping agent") in fiber-optic cables. Also used in some nuclear control rods, metallic alloys, and to color specialized glass and porcelain in sunglasses and cheap jewelry.
Thulium: The rarest of all naturally occurring rare earth metals. Has few commercial applications, although it is used in some surgical lasers. After being exposed to radiation in nuclear reactors, it's also used in portable X-ray technology.
Ytterbium: Used in some portable X-ray devices, but otherwise has limited commercial uses. Among its specialty applications, it's used in certain types of lasers, stress gauges for earthquakes, and as a doping agent in fiber-optic cables.
Lutetium: Mainly restricted to specialty uses, such as calculating the age of meteorites or performing positron emission tomography (PET) scans. Has also been used as a catalyst for the process of "cracking" petroleum products at oil refineries.
Nice to meet you Rare Earth Metals! But I guess I'll just stick to the common metals as I have difficulty in memorizing you guys.
What we just have to remember is even though these rare earth metals are not that rare but continuous use would cause depletion of natural resources. So the key here is to Reduce our needs for it, Reuse as much as possible and Recycle everything!