Element Thulium, Tm, Lanthanide

Marignac's erbia was the following year split by Per Teodor Cleve into erbia proper and two new elements, which he named thulium and holmium. He asked Lars Fredrik Nilson to tale the residue of scandium and ytterbium extraction supposing that it is a relatively pure erbium salts solution. However, after hundreds of repeated operations of precipitating and dissolving it turned out that erbium still contained some impurity. Cleve made a request for Talen, the professor of physics in Uppsala University to investigate the absorption spectra of these fractions. Talen found lines which belonged to erbium and holmium; the third spectrum belonged to a new element. Thus thulium was discovered, named by Cleve after Scandinavia - Thule.

According to academic A.P. Vinogradov, lanthanide thulium is the rarest among all rare earth elements except promethium. Its crustal abundance is 8x10^-5 mass % (2.7x10^-5%), in sea water 1x10^-7 mg/L. As other rare earth elements thulium is contained in many minerals, including xenotime, euxenite, monazite, bastnasite, loparite and others.