Definition of the Thulium Element A bright, silvery rare-earth element and can be cut by a knife. It slowly tarnishes in air, but is more resistant to oxidation than most rare-earth elements. It also has some corrosion resistance in dry air and good ductility. It is obtained commercially from monazite, having an x-ray emitting isotope that is used in small portable medical x-ray units. The Atomic Number of this element is 69 and the Element Symbol is Tm. Origin / Meaning of the name Thulium Named after Thule, an ancient Roman name for a mythical country in the far north, possibly Scandinavia. Facts about the Discovery and History of the Thulium Element Thulium was discovered by Per Teodor Cleve in Sweden in 1879 History of the Periodic Table Check out the brief History of the Periodic Table which details dates and the names of famous scientists and chemists who contributed to the development of the Periodic Table. Occurrence of the Thulium Element Found in small quantities in minerals with other rare earths - gadolinite, euxenite, xenotime Abundances of the element in different environments % in Universe 1×10-8% % in Sun 2×10-8% % in Meteorites 2.9×10-6% % in Earth's Crust 0.000045% % in Oceans 2×10-11% % in Humans N/A Associated Uses of Thulium Lasers Power for portable x-ray machines |