Thulium REE Collection rare earth metals elements


Thulium, the rarest of the rare earths, is named for the land of the far North, Thule. It elicits visions of brightly dressed Sámi people, ice fishing, fur trading, and furry Samoyeds herding reindeer across the Arctic’s frozen expanse. As the fifth member of the heavy-group rare-earth elements (HREE), thulium has five paired electrons giving it the ability to fluoresce to reduce X-ray exposure, illuminate sport arenas and athletic fields, and generate laser beams that provide less invasive surgical procedures.


  • Lanthanum oxybromide activated with thulium is the leading X-ray intensifying screen phosphor that minimizes radiation exposure during medical and dental procedures.
  • Metal halide lamps using thulium iodide along with dysprosium and holmium iodides are used in sports stadium illumination, movie and stage lighting, and commercial interior-exterior lighting.
  • Lasers using chromium, thulium, holmium: yttrium aluminum garnet (Cr,Tm,Ho:YAG) are used in surgery, dentistry, atmospheric testing, and remote sensing.
  • Thulium:Glass lasers are used in open, laparoscopic, and endoscopic medical procedures to cut and cauterize.

Interesting Facts

  • In, 1965, the first Tm:YAG laser at 2 μm was a flash lamp pumped laser which operated at a very cold temperature of -196 °C.
  • In 1975, the first pulsed laser to operate at room temperature used a Cr,Tm:YAG crystal.
  • Phillips Lighting created the first “compact” metal halide lamp using thulium in 1985. The experimental “Thulium Lamp,” as it was called, was produced to provide improved neutral white light for commercial interior lighting.


Thulium was discovered by Swedish chemist, geologist, botanist, and hydrogapher Per Teodor Cleve in 1879. He obtained an impure erbia from which scandia and ytterbia had been removed and noticed that the atomic weight of his impure erbia did not match that of erbia discovered by Carl Mosander in 1843. He immediately started refining it by fractional crystallization into three “earths”, erbia, holmia, and thulia (Weeks and Leicester, 1968, p. 681). Holmium and thulium were both new rare earths that Cleve verified by molecular weight and their spectral lines (Cleve, 1879). Per Teodor Cleve proposed the name thulium, “derived from Thule, the most ancient name of Scandinavia.”


Thulium is a bright silvery metal that is reasonably stabile in air. It is soft, malleable, and can be cut with a knife. Thulium has one stable isotope and 31 radioisotopes. It has a hexagonal close-packed structure, a density of 9.321 gm/cm3, a melting point of 1545 °C, and a boiling point of 1950 °C. Thulium oxide, or thulia, occurs as a sesquioxide with the formula Tm2O3, and exhibits its most common valence state of +3, however, valence states of +2 and +4 have been observed in several compounds. The oxide is a pale green powder with a specific gravity of 8.6 gm/cm3, a melting point of 2425 °C, and a formula weight of 385.87.

Preparation of Metal

Thulium metal is typically prepared by metallothermic reduction of the oxide, since it will not reduce from the trihalide because of its high vapor pressure. This is similar to the procedure for Sm, Eu, and Yb. The oxide is is heated in air to 950 °C for 15 hours to drive off absorbed moisture, carbon dioxide, and other compounds. Thulium oxide is reduced with lanthanum metal turnings (15% in excess of theoretical amount) by volatilization within a tantalum crucible with an attached tantalum condenser. The reactants are heated in a vacuum reduction furnace by slowing raising the temperature to 1600 °C and held at temperature for several hours (Beaudry and Gschneidner, Jr., 1978). Thulium metal is formed starting at 950 °C when the oxide preferentially separates from the thulium oxide and combines with the lanthanum metal forming lanthanum oxide and forms a sublimated thulium metal within the tantalum condenser.


Small resources of thulium in xenotime and synchisite-(Y) are available worldwide in ancient and recent placer deposits, uranium ores, vein deposits with tungsten, alkalic igneous, and weathered clay deposits (ion-adsorption ore). It occurs in the Earth’s crust at an average concentration of 0.5 parts per million. Xenotime is enriched in thulium oxide and contains 1.1% to 1.3% of the rare-earth oxide (REO) content. Monazite-(Ce), which is more abundant in the Earth’s’ crust than xenotime, has only trace amounts of thulium and is not an economic source. The yttrium-enriched Longnan-type ion-adsorption ore has a thulium oxide content of 0.13% to 0.7% of the REO total, and the Xunwu-type contains from trace amounts to 0.3%. Thulium oxide only occurs in trace amounts in the bastnäsites at the Bayan Obo mine in China and at Mountain Pass, California, in the United States and is not an economic source. Subeconomic resources of thulium occur in apatite-magnetite-bearing rocks, eudialyte-bearing deposits, deposits of niobium-tantalum minerals, non-placer monazite-bearing deposits, sedimentary phosphate deposits, and uranium ores. Additional subeconomic resources in Canada are contained in allanite, apatite, and britholite at Eden Lake, Manitoba; allanite and apatite at Hoidas Lake, Saskatchewan; fergusonite and xenotime at Nechalacho (Thor Lake), Northwest Territories; and eudialyte-(Y), mosandrite, and britholite at Kipawa, Quebec. It occurs in low concentrations in various minerals in differing concentrations and occurs in a wide variety of geologic environments, including alkaline granites and intrusives, hydrothermal deposits, laterites, placers, and vein-type deposits (Hedrick, 2010).


Thulium is mined from a variety of ore minerals and deposits using various methods. Xenotime and monazite are recovered from heavy-mineral sands (specific gravity >2.9) deposits in various parts of the world as a byproduct of mining zircon and titanium-minerals or tin minerals. Heavy mineral sands are recovered by surface placer methods from unconsolidated sands. Many of these deposits are mined using floating dredges which separate the heavy-mineral sands from the lighter weight fraction with an on-board wet mill through a series of wet-gravity equipment that includes screens, hydrocyclones, spirals, and cone concentrators. Consolidated or partially consolidated sand deposits that are too difficult to mine by dredging are mined by dry methods. Ore is stripped by typical earth-moving equipment with bulldozers, scrapers, and loaders or by water jet methods. Ore recovered by these methods is crushed and screened and then processed by the wet mill described above. Wet mill heavy-mineral concentrate is sent to a dry mill for processing to separate the individual heavy-minerals using a combination of scrubbing, drying, screening, electrostatic, electromagnetic, magnetic, and gravity processes (Hedrick, 1991). Vein monazite has been mined by hard-rock methods in South Africa and the United States, and as a byproduct of tungsten mining in China (Hedrick, 2010).

In Russia, loparite is mined by underground methods using room and pillar methods. Ore is drilled and blasted and removed from the mine. At the mill the blasted ore is crushed, screened, and processed by flotation to produce a loparite concentrate with a 0.1% Tm2O3 content. In Kyrgyzstan, synchysite-(Y) concentrate with a Tm2O3 content of 0.25% to 0.3% was mined by hard-rock methods from the open-pit Kutessai-II deposit near Aktyuz (Hedrick, Sinha, and Kosynkin, 1997). Argillaceous marine sediments enriched in fossil fish remains at the Melovie deposit in Kazakhstan were previously recovered for their uranium and rare-earth content, including thulium. The main source of the world’s thulium is the ion-adsorption lateritic clays in the southern provinces of China, primarily Fujian, Guangdong, and Jiangxi, with a lesser number of deposits in Guangxi and Hunan. These deposits are mined by leaching methods (Hedrick, 2010).

Selected thulium-bearing minerals

Xenotime Y(PO4)
Synchysite-(Y) Ca(Y,Ce)(CO3)2F
Eudialyte-(Y) Na4(Ca,Ce)2(Fe2+,Mn,Y)ZrSi8O22(OH,Cl)2
Gadolinite-(Y) Y2Fe2+Be2(Si2O10)
Mosandrite Na2Ca4(REE)(Si2O7)2OF3
Britholite-(Y) Ca2(Y,Ca)3(SiO4,PO4)3(OH,F)
Ion adsorption lateritic clays Y-enriched lateritic clays


Beaudry and Bernard J. and Karl A. Gschneidner, Jr., 1978, Preparation and Basic Properties of the Rare Earth Metals: chapter 2 in Handbook of the Physics and Chemistry of Rare Earths-Volume 1:Metals, (Gschneidner, Jr. and Eyring, editors), North-Holland, New York, p. 173-232.

Cleve, Per Teodor, 1879, Sur deux nouveaux éléments dans l’erbine [On two new elements with erbia]: Comptes Reudus, July 7, no. 1, p. 478-481.

Gschneidner, Karl A. Jr., 2011, The Rare Earth Crisis—The Supply/Demand Situation for 2010-2015: article in Material Matters, Aldrich Chemical Co., Milwaukee, Wisconsin, v. 6, no. 2, p. 34-35.

Hedrick, James B., 2010, Rare earths: chapter in Mineral commodity summaries 2010, U.S. Geological Survey, p. 128-129.

Hedrick, James B., 1990, Rare earths—The lanthanides, yttrium, and scandium: chapter in Minerals Yearbook 1990, U.S. Geological Survey, v. 1, p. 903-922.

Hedrick, James B., 1991, Rare earths—The lanthanides, yttrium, and scandium: chapter in Minerals Yearbook 1991, U.S. Geological Survey, v. 1, p. 1211-1237.

Hedrick, James B., 2010, Yttrium: chapter in Mineral commodity summaries 2010, U.S. Geological Survey, p. 182-183.

Hedrick, James B., Shyama P. Sinha, and Valery D. Kosynkin, 1997, Loparite—a rare-earth ore (Ce,Na,Sr,Ca)(Ti,Nb,Ta,Fe+3)O3: Journal of Alloys and Compounds, v. 250, p. 467-470.

Weeks, Mary E., and Henry M. Leicester, 1968, Discovery of the Elements (7th ed.): Easton, Pennsylvania, Journal of Chemical Education, 896 p.

Electrons per shell:
2, 8, 18, 31, 8, 2
Atomic number,
Protons, Electrons:
Number of Neutrons:
Atomic Mass:
168.9342 amu
Melting Point:
1545 °C
Boiling Point:
1950 °C
Density @ 293 K:
9.321 g/cm3
Crystal structure: