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thulium (Tm)

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A lustrous, silver-white, metallic element; it is the least abundant member of the lanthanide series. First discovered in 1879, its chief ore is monazite. Soft, malleable, and ductile, thulium combines with oxygen and the halogens. It is used in arc lighting; thulium-170, which emits X-rays, is used in portable X-ray units. Its most common isotope is 169Tm (100%).

atomic number 69
relative atomic mass 168.934
relative density 9.31
melting point 1,545°C (2,813°F)
boiling point 1,947°C (3,537°F)

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