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Thulium is a chemical element, having the chemical symbol Tm. Its atomic number (the number of protons) is 69. It has a standard atomic weight of 168.9342 g•mol −1 and is a solid in its elemental form.
Thulium is considered a member of the "Lanthanide" class of elements. At a pressure of 101.325 kPa, it has a boiling point of 1,950°C and a melting point of 1,545 °C.