holmium [key] [Lat.,=Stockholm], metallic chemical element; symbol Ho; at. no. 67; at. wt. 164.93032; m.p. about 1,474℃; b.p. about 2,425℃; sp. gr. 8.78 at 25℃; valence +3. Holmium is a soft, malleable, lustrous, silvery metal of the lanthanide series in Group 3 of the periodic table. It is prepared by reduction of a holmium halide with calcium metal. Holmium is stable in dry air at room temperature but is rapidly oxidized in moist air or when heated. Holmia, the oxide, is found in nature, with other rare earths, in the minerals gadolinite and monazite. Holmium, its oxide, and its salts have no commercial uses. The metal was discovered spectroscopically in 1878 by the Swiss chemists Soret and Delafontaine and independently in 1879 by the Swedish chemist Per T. Cleve; it is named for Cleve's native city.
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