Editing Thulium (section)

==Occurrence==
[[File:Monazit - Madagaskar.jpg|thumb|Thulium is found in the mineral monazite]]
The element is never found in nature in pure form, but it is found in small quantities in [[mineral]]s with other rare earths. Thulium is often found with minerals containing [[yttrium]] and [[gadolinium]]. In particular, thulium occurs in the mineral [[gadolinite]].<ref name= "handbook of metals">{{cite book|author=Walker, Perrin|author2=Tarn, William H.|name-list-style=amp |title=CRC Handbook of Metal Etchants|url=https://books.google.com/books?id=-2ObmTZTq2QC&pg=PA1241|date=2010|publisher=CRC Press|isbn=978-1-4398-2253-1|pages=1241–}}</ref> Like many other [[lanthanides]], thulium also occurs in the minerals [[monazite]], [[xenotime]], and [[euxenite]]. Thulium has not been found in prevalence over the other rare earths in any mineral yet.<ref>{{cite web |url=https://www.mindat.org/ |title=Mindat.org |author=Hudson Institute of Mineralogy |date=1993–2018 |website=www.mindat.org |access-date=14 January 2018}}</ref> Its [[Abundance of elements in Earth's crust |abundance in the Earth's crust]] is 0.5&nbsp;mg/kg by weight.<ref name=CRCAbundanceTable>ABUNDANCE OF ELEMENTS IN THE EARTH’S CRUST AND IN THE SEA, ''CRC Handbook of Chemistry and Physics,'' 97th edition (2016–2017), p. 14-17</ref> 

Thulium makes up approximately 0.5 parts per million of [[soil]], although this value can range from 0.4 to 0.8 parts per million. Thulium makes up 250 parts per quadrillion of [[seawater]].<ref name="history">{{cite book |pages=442–443 |url= https://books.google.com/books?id=Yhi5X7OwuGkC&pg=PA442 |title= Nature's building blocks: an A-Z guide to the elements |author= Emsley, John |publisher=Oxford University Press |location= US |date= 2001 |isbn= 0-19-850341-5}}</ref> In the [[Solar System]], thulium exists in concentrations of 200 parts per trillion by weight and 1&nbsp;part per trillion by moles.<ref name="cool" /> Thulium ore occurs most commonly in [[China]]. [[Australia]], [[Brazil]], [[Greenland]], [[India]], [[Tanzania]], and the [[United States]] also have large reserves of thulium. In 2001, the total world reserves of thulium were approximately 100,000 [[tonne]]s. Thulium is the least abundant [[lanthanide]] on Earth except for the radioactive [[promethium]].<ref name="history" />