The rarest stable lanthanide, yet surprisingly useful. Thulium is a soft, silvery metal found at just 0.5 ppm in Earth's crust. Its radioactive isotope thulium-170 produces X-rays without any power outlet. Imagine: a tiny source replacing a bulky X-ray machine.
Swedish chemist Per Teodor Cleve discovered thulium in 1879 and named it after Thule — the legendary northern land of ancient Greek mythology. Today, thulium lasers cut tissue with surgical precision, while thulium-doped fiber amplifiers boost internet signals across thousands of kilometers.
Thulium has only one stable isotope — Tm-169 — making it a monoisotopic element. Its density is 9.32 g/cm³, similar to nickel. It melts at 1,545 °C. In nature, thulium hides inside monazite and bastnaesite minerals, always mixed with other lanthanides. Separating them is extremely difficult.
Global thulium production is only a few dozen tons per year. That's why a kilogram of pure thulium costs $3,000 to $5,000. The main producers are China, Brazil, and India.
Metallic thulium has low toxicity and is safe during normal handling. However, fine thulium dust is flammable and explosive, and can irritate eyes and lungs. Soluble thulium compounds may accumulate in the liver if ingested. Radioactive thulium-170 requires lead shielding and dosimetric monitoring. Powdered thulium should be handled in a fume hood with a respirator.
Thulium is the rarest stable lanthanide. Earth's crust contains just 0.5 ppm — less than gold in seawater.
The name 'thulium' comes from Thule — the ancient Greek name for a mysterious land at the far north. The element was discovered in Sweden in 1879.
The isotope thulium-170 emits X-rays without electricity. Portable X-ray devices based on it work in jungles and war zones alike.
Thulium lasers cut soft tissue with micrometer precision. Surgeons use them for kidney, prostate, and urological operations.
Thulium has just one stable isotope — Tm-169. This makes it a monoisotopic element, which is rare among metals.
Over 90% of the world's thulium is mined in China. A kilogram of pure thulium costs $3,000 to $5,000.
| Isotope | Mass (u) | Abundance | Half-life | Decay |
|---|---|---|---|---|
169Tm | 168.934213 | 100.00% | stable | — |
Separation from erbia