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This is thulium.

Symbol Tm
Atomic number 69
Atomic mass 168.9342 amu

Thulium, is the least abundant of all the naturally occurring rare-earths. The only rare-earth that is any rarer is promethium because it never occurs in nature.

Distinguishing properties

Thulium is a soft malleable ductile and silvery element of the lanthanide series. It occurs in association with yttrium in a number of ores such as xenotime and euxenite found in monoazite sands.


Thulium has few important uses. Thulium produces an isotope that emits x-rays. Small pellets can be used as a portable source of diagnostic x-rays for medical use. Another application of thulium is in magnetic ceramic materials.

See also

Periodic table of the elements