<P> Despite their name, rare - earth elements are--with the exception of the radioactive promethium--relatively plentiful in Earth's crust, with cerium being the 25th most abundant element at 68 parts per million, or more abundant than copper . They are not especially rare, but they tend to occur together in nature and are difficult to separate from one another . However, because of their geochemical properties, rare - earth elements are typically dispersed and not often found concentrated as rare - earth minerals in economically exploitable ore deposits . The first such mineral discovered was gadolinite, a mineral composed of cerium, yttrium, iron, silicon and other elements . This mineral was extracted from a mine in the village of Ytterby in Sweden; four of the rare - earth elements bear names derived from this single location . </P> <P> A table listing the 17 rare - earth elements, their atomic number and symbol, the etymology of their names, and their main usages (see also Applications of lanthanides) is provided here . Some of the rare - earth elements are named after the scientists who discovered or elucidated their elemental properties, and some after their geographical discovery . </P> <Table> <Tr> <Th> Z </Th> <Th> Symbol </Th> <Th> Name </Th> <Th> Etymology </Th> <Th> Selected applications </Th> </Tr> <Tr> <Th> </Th> <Th> </Th> <Th> </Th> <Th> </Th> <Th> </Th> </Tr> <Tr> <Td> 21 </Td> <Td> Sc </Td> <Td> Scandium </Td> <Td> from Latin Scandia (Scandinavia). </Td> <Td> Light aluminium - scandium alloys for aerospace components, additive in metal - halide lamps and mercury - vapor lamps, radioactive tracing agent in oil refineries </Td> </Tr> <Tr> <Td> 39 </Td> <Td> Y </Td> <Td> Yttrium </Td> <Td> after the village of Ytterby, Sweden, where the first rare earth ore was discovered . </Td> <Td> Yttrium aluminium garnet (YAG) laser, yttrium vanadate (YVO) as host for europium in television red phosphor, YBCO high - temperature superconductors, yttria - stabilized zirconia (YSZ), yttrium iron garnet (YIG) microwave filters, energy - efficient light bulbs, spark plugs, gas mantles, additive to steel, cancer treatments </Td> </Tr> <Tr> <Td> 57 </Td> <Td> La </Td> <Td> Lanthanum </Td> <Td> from the Greek "lanthanein", meaning to be hidden . </Td> <Td> High refractive index and alkali - resistant glass, flint, hydrogen storage, battery - electrodes, camera lenses, fluid catalytic cracking catalyst for oil refineries </Td> </Tr> <Tr> <Td> 58 </Td> <Td> Ce </Td> <Td> Cerium </Td> <Td> after the dwarf planet Ceres, named after the Roman goddess of agriculture . </Td> <Td> Chemical oxidizing agent, polishing powder, yellow colors in glass and ceramics, catalyst for self - cleaning ovens, fluid catalytic cracking catalyst for oil refineries, ferrocerium flints for lighters </Td> </Tr> <Tr> <Td> 59 </Td> <Td> Pr </Td> <Td> Praseodymium </Td> <Td> from the Greek "prasios", meaning leek - green, and "didymos", meaning twin . </Td> <Td> Rare - earth magnets, lasers, core material for carbon arc lighting, colorant in glasses and enamels, additive in didymium glass used in welding goggles, ferrocerium firesteel (flint) products . </Td> </Tr> <Tr> <Td> 60 </Td> <Td> Nd </Td> <Td> Neodymium </Td> <Td> from the Greek "neos", meaning new, and "didymos", meaning twin . </Td> <Td> Rare - earth magnets, lasers, violet colors in glass and ceramics, didymium glass, ceramic capacitors, electric motors of electric automobiles </Td> </Tr> <Tr> <Td> 61 </Td> <Td> Pm </Td> <Td> Promethium </Td> <Td> after the Titan Prometheus, who brought fire to mortals . </Td> <Td> Nuclear batteries, luminous paint </Td> </Tr> <Tr> <Td> 62 </Td> <Td> Sm </Td> <Td> Samarium </Td> <Td> after mine official, Vasili Samarsky - Bykhovets . </Td> <Td> Rare - earth magnets, lasers, neutron capture, masers, control rods of nuclear reactors </Td> </Tr> <Tr> <Td> 63 </Td> <Td> Eu </Td> <Td> Europium </Td> <Td> after the continent of Europe . </Td> <Td> Red and blue phosphors, lasers, mercury - vapor lamps, fluorescent lamps, NMR relaxation agent </Td> </Tr> <Tr> <Td> 64 </Td> <Td> Gd </Td> <Td> Gadolinium </Td> <Td> after Johan Gadolin (1760--1852), to honor his investigation of rare earths . </Td> <Td> High refractive index glass or garnets, lasers, X-ray tubes, computer memories, neutron capture, MRI contrast agent, NMR relaxation agent, magnetostrictive alloys such as Galfenol, steel additive </Td> </Tr> <Tr> <Td> 65 </Td> <Td> Tb </Td> <Td> Terbium </Td> <Td> after the village of Ytterby, Sweden . </Td> <Td> Additive in Neodymium based magnets, green phosphors, lasers, fluorescent lamps, magnetostrictive alloys such as terfenol - D, naval sonar systems, stabilizer of fuel cells </Td> </Tr> <Tr> <Td> 66 </Td> <Td> Dy </Td> <Td> Dysprosium </Td> <Td> from the Greek "dysprositos", meaning hard to get . </Td> <Td> Additive in Neodymium based magnets, lasers, magnetostrictive alloys such as terfenol - D, hard disk drives </Td> </Tr> <Tr> <Td> 67 </Td> <Td> Ho </Td> <Td> Holmium </Td> <Td> after Stockholm (in Latin, "Holmia"), native city of one of its discoverers . </Td> <Td> Lasers, wavelength calibration standards for optical spectrophotometers, magnets </Td> </Tr> <Tr> <Td> 68 </Td> <Td> Er </Td> <Td> Erbium </Td> <Td> after the village of Ytterby, Sweden . </Td> <Td> Infrared lasers, vanadium steel, fiber - optic technology </Td> </Tr> <Tr> <Td> 69 </Td> <Td> Tm </Td> <Td> Thulium </Td> <Td> after the mythological northern land of Thule . </Td> <Td> Portable X-ray machines, metal - halide lamps, lasers </Td> </Tr> <Tr> <Td> 70 </Td> <Td> Yb </Td> <Td> Ytterbium </Td> <Td> after the village of Ytterby, Sweden . </Td> <Td> Infrared lasers, chemical reducing agent, decoy flares, stainless steel, stress gauges, nuclear medicine, monitoring earthquakes </Td> </Tr> <Tr> <Td> 71 </Td> <Td> Lu </Td> <Td> Lutetium </Td> <Td> after Lutetia, the city that later became Paris . </Td> <Td> Positron emission tomography--PET scan detectors, high - refractive - index glass, lutetium tantalate hosts for phosphors, catalyst used in refineries, LED light bulb </Td> </Tr> </Table> <Tr> <Th> Z </Th> <Th> Symbol </Th> <Th> Name </Th> <Th> Etymology </Th> <Th> Selected applications </Th> </Tr>

What is the rarest element found on earth