![Thulium element card: symbol Tm, atomic number 69, atomic mass 168.93, electron configuration [Xe] 4f¹³ 6s², oxidation states +3, Lanthanide, f-block, period 6, solid at room temperature.](https://stage.chemistry-dictionary.com/wp-content/uploads/2026/09/thulium-chemical-element.webp)
Mining companies mostly extract thulium from monazite and bastnasite ores found underground. It sits mixed alongside other rare earth elements in very tiny amounts. Thulium makes up only about 0.5 parts per million of the Earth’s crust.
It sits near the end of the f-block on the modern periodic table. The metal behaves very much like its closest neighboring lanthanide elements. It almost always loses three electrons to form a +3 oxidation state.
The solid metal stays reasonably stable when exposed to dry atmospheric air. However, you must carefully protect it from moisture to stop it from breaking down. Thulium will burn in the air at high temperatures to form thulium(III) oxide.
The metal also dissolves very quickly when placed into a dilute acid. This acidic reaction creates a liquid solution with a pale green color. Scientists can take natural thulium-169 and place it inside a nuclear reactor.
Bombarding the atoms with neutrons creates a radioactive isotope called thulium-170. This specific radioactive isotope constantly releases a steady stream of X-rays. Thulium is extremely scarce and costs a massive amount of money to extract.
Therefore, the pure metal has very few commercial uses outside of specialized scientific research. However, it has a unique ability to emit specific colors of bright light.