Presently,Rare earth elements are relatively plentiful and valuable in the earth's crust, with cerium being the 25th most abundant element at 68 parts per million. This makes it as abundant as copper. Because of their geochemical properties, rare earth elements are typically dispersed. It means they are often found in concentrated enough clusters to make them viable to mine. It was the scarcity of these minerals that led to them being called rare earths. Rare earths are categorised into light elements (lanthanum to samarium) and heavy elements (europium to lutetium). The latter are less common and consequently much more expensive.

Chemically, rare earths are strong reducing agents. Their compounds are generally ionic and they display high melting and boiling points. Rare earths are relatively soft when in their metallic state while those with a higher atomic number tend to be harder. Rare earths react with other metallic and non-metallic elements to form compounds each of which has specific chemical behaviours. This makes them indispensable and non-replaceable in many electronic, optical, magnetic, ceramic, and catalytic applications. Rare earth compounds are commonly fluorescent under ultraviolet light, which can assist in their identification. Rare earths also react with water or diluted acid to produce hydrogen gas.

Summary of Rare Earth Elements and their Applications

Summary of Rare Earths Compounds and their Applications

Summary of Rare Earths and their key attributes 

Scandium or Sc (21) – is a silvery-white metal and a non-lanthanide rare earth. It is used in many popular consumer products such as televisions and fluorescent, energy-saving bulbs. Its main industrial use is to help strengthen metal compounds. The only concentrated sources of scandium currently known are in rare minerals such as thortveitite, euxenite, and gadolinite.

Yttrium or Y (39) - is a non-lanthanide rare earth element used in to produce superconductors, powerful pulsed lasers, cancer treatment drugs, rheumatoid arthritis medicines, and surgical supplies. Silvery metal in colour, it is also used in many popular consumer products such as televisions and camera lenses.

Lanthanum or La (57) – is a silver-white metal that is one of the most reactive rare earth elements. It is used in the manufacture of specialised optical glasses including infrared absorbing glass as well as camera and telescope lenses. It can also be used to help make steel more malleable. Other applications for lanthanum include wastewater treatment and petroleum refining.

Cerium or Ce (58) – is a silvery-white metal that easily oxidises in the air. It is the most abundant rare earth elements and has many uses including as a catalyst in catalytic converters in automotive exhaust systems to reduce emissions. It is also a key component for precision glass polishing. Cerium can also be used in iron, magnesium and aluminium alloys, magnets, certain types of electrodes, and carbon-arc lighting.

Praseodymium or Pr (59) – this soft, silvery metal was first used to create a yellow-orange stain for ceramics. Although it is still used to colour certain types of glasses and gemstones, praseodymium is primarily used in rare earth magnets.  It can also be found in applications as diverse as creating high-strength metals found in aircraft engines and flint for starting fires.

Neodymium or Nd (60) – is a soft, silvery metal, neodymium that is used with praseodymium to create some of the strongest permanent magnets available in the world today. These magnets are found in most modern vehicles and aircraft as well as popular consumer electronics such as headphones, microphones, and computer discs. Neodymium is also used to make high-powered, infrared lasers for industrial and defence applications.

Promethium or Pm (61) – is the only naturally radioactive rare earth element. Virtually all promethium in the earth's crust has long ago decayed into other elements. Today, it is largely artificially created, and used in watches, pacemakers, and a scientific research applications.

Samarium or Sm (62) – is a silvery metal that can be used in several vital ways including as in very powerful magnets for transportation, defence, and commercial technologies. In conjunction with other compounds, it can also be used for intravenous radiation treatments to kill cancer cells. It is also used to help treat lung, prostate, breast, and some forms of bone cancer. Because it is a stable neutron absorber, samarium is also used to control the rods of nuclear reactors.

Europium or Eu (63) – is a hard metal used to create visible light in compact fluorescent bulbs and colour displays such as in LCD televisions. It is also used to make the special phosphors marks on the Euro notes to help prevent counterfeiting.

Gadolinium or Gd (64) – has particular properties that make it especially suitable for shielding in nuclear reactors and neutron radiography. It is also used to help target tumours in neuron therapy as well as enhance magnetic resonance imaging (MRI). X-rays and bone density tests also use gadolinium, making this rare earth element a major contributor to modern health care solutions.

Terbium or Tb (65) – is a silvery rare earth metal that is so soft it can be cut with a knife. Terbium is often used in compact fluorescent lighting, colour displays, and as an additive to permanent rare earth magnets so they can function better under higher temperatures. It can also be found in fuel cells designed to operate at elevated temperatures and some electronic devices as well as naval sonar systems. Terbium in its alloy form has the highest magnetostriction of any such substance. Because of its magnetisation, in its alloy form it is easy to change its shape, making it vital component of Terfenol-D which is used in many defence and commercial technologies.

Dysprosium or Dy (66) – is a soft, silver metal with one of the highest magnetic strengths of all of the rare earths, matched only by holmium. Dysprosium is often added to permanent rare earth magnets to help them operate more efficiently at higher temperatures. Lasers and commercial lighting use dysprosium as do hard computer disks and other electronics which require certain magnetic properties. Dysprosium can also be used in nuclear reactors and modern, energy-efficient vehicles.

Holmium or Ho (67) – has incredible magnetic properties. In fact, some of the strongest artificially created magnetic fields are the result of magnetic flux concentrators made with holmium alloys. As well as providing colouring to cubic zirconia and glass, holmium can also be used in nuclear control rods and microwave equipment.

Erbium or Er (68) – is widely used in nuclear applications such as neutron-absorbing control rods. It is a key component of high-performance fibre optic communications systems. It can also be used to provide glass and other materials a pink colour for aesthetic as well as specific industrial purposes. Erbium is also used to help create lasers, including those for specific medical applications.

Thulium or Tm (69) – is a silvery-grey metal and one of the least abundant rare earths. Its isotopes are widely used as the radiation device in portable X-rays which makes thulium a highly useful material. Thulium is also a component of highly efficient lasers which are used in the defence, medical, and meteorology sectors.

Ytterbium or Yb (70) - has several important uses in health care including in certain cancer treatments. Ytterbium can also enhance stainless steel as well as help monitor the effects of earthquakes and explosions on the ground.

Lutetium or Lu (71) – is the last of the rare earth elements (in order of their atomic number) and has several interesting uses. For example, lutetium isotopes can help reveal the age of ancient items such as meteorites. It also has applications related to petroleum refining and positron emission tomography. Experimentally, lutetium isotopes have also been used to target certain types of tumours.