(named after Ytterby, a village in Sweden) Discovered by Mosander in1843. Found in cerite, gadolinite and monazite. Isolated only recently.
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silvery-gray, rare earth metal, malleable, ductile, soft, can be cut with a knife, fairly stable in air, 19 isotopes
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used as a laser material, used in doping (adding impurities to semiconductors) of solid state devices, potential use in color TV tubes as an phosphor activator