Thulium is a chemical element that has the symbol Tm and atomic number 69. Thulium is the least abundant of the lanthanides. It is an easily workable metal with a bright silvery-grey luster. Despite its high price and rarity, thulium is used as the radiation source in portable X-ray devices and in solid-state lasers.


It is reasonably stable in air, but should be protected from moisture. The metal is soft, malleable, and ductile. Thulium is ferromagnetic below 32 K, antiferromagnetic between 32 and 56 K and paramagnetic above 56K. Thulium metal tarnishes slowly in air and burns readily at 150 °C to form thulium(III) oxide, it is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form thulium hydroxide: Thulium reacts with all the halogens, reactions are slow at room temperature, but are vigorous above 200 °C it dissolves readily in dilute sulphuric acid to form solutions containing the pale green Tm(III) ions, which exist as a [Tm(OH2)9]3+ complexes. Thulium reacts with various metallic and non-metallic elements forming a range of binary compounds, including TmN, TmS, TmC2, Tm2C3, TmH2, TmH3, TmSi2, TmGe3, TmB4, TmB6 and TmB12. In those compounds, thulium exhibits valence states +2, +3 and +4, however, the +3 state is most common and only this state has been observed in Tm solutions

Naturally occurring thulium is composed of one stable isotope, Tm-169 (100% natural abundance). Thirty one radioisotopes have been characterized, with the most stable being Tm-171 with a half-life of 1.92 years, Tm-170 with a half-life of 128.6 days, Tm-168 with a half-life of 93.1 days, and Tm-167 with a half-life of 9.25 days. All of the remaining radioactive isotopes have half-lives that are less than 64 hours, and the majority of these have half-lives that are less than 2 minutes. This element also has 14 meta states, with the most stable being Tm-164m (t½ 5.1 minutes), Tm-160m (t½ 74.5 seconds) and Tm-155m (t½ 45 seconds).

The isotopes of thulium range in atomic weight from 145.966 u (Tm-146) to 176.949 u (Tm-177). The primary decay mode before the most abundant stable isotope, Tm-169, is electron capture, and the primary mode after is beta emission. The primary decay products before Tm-169 are element 68 (erbium) isotopes, and the primary products after are element 70 (ytterbium) isotopes.


The base value of each unit of ranges between 10 and 45Ð per unit, with up to 3 units being found at any one time.

Presence on Mars: Very Rare

Martian Minerals
Group 1 | Group 2 | Group 3 | Group 4 | Group 5 | Group 6
Group 4 |Actininum | Areanetium | Borane | Carbon Tetrachloride | Dubnium | Dysprosium | Erbium | Europium | Ferrous Dixenate | |Gadollinium | Golgathium | Holmium | Holmium Sulfate | Iron Golgathide | Neodymium | Praseodymium | Promethium | |Protactinium | Rutherfordium | Samarium | Selenium Arsenide | Terbium | Thallium Titanide | Thulium | Uranium|

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