A lustrous, silver-white, metallic element;
it is the least abundant member of the lanthanide
series. First discovered in 1879, its chief ore is monazite.
Soft, malleable, and ductile, thulium
combines with oxygen and the halogens.
It is used in arc lighting; thulium-170, which emits X-rays,
is used in portable X-ray units. Its most common isotope
is 169Tm (100%).
|relative atomic mass