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.