Characteristics: Pure thulium metal has a bright, silvery luster. It slowly tarnishes in air and reacts slowly with water. Soluble in dilute acids. Salts colored green.
The metal is malleable and ductile, has a Mohs hardness of 2 to 3 and can be cut with a knife. Thulium is ferromagnetic below 32 K, antiferromagnetic between 32 and 56 K, and paramagnetic above 56 K. Liquid thulium is very volatile.
It is the thirteenth and antepenultimate element in the lanthanide series. Thulium is the second least abundant of the lanthanides after promethium, which is only found in trace quantities on Earth. Despite its high price and rarity, thulium is used as the radiation source in portable X-ray devices and in solid-state lasers. It has no significant biological role and is not particularly toxic.
Hazard: Fire risk in dust form.