Rare earth elements make the strongest batteries and magnets for big scale items like cars and wind turbines, but also small consumer electronic devices. Smartphones, mp3 players and earphone speakers all use tiny magnets made from neodymium and samarium.
Back when production at the Mountain Pass Mine was in its prime, one of the most valuable elements mined was europium. Early TVs used a compound containing europium because the metal is something called a red phosphor--meaning it glows red when hit with an electron beam.
Europium also makes a blue phosphor that's currently used for plasma screen TVs. Another rare earth element called terbium is used to make a green-glowing phosphor. All three colors are used in LED screens.
Rare earths also make those screens look good. They have the perfect chemical composition to polish glass, so cathode ray tubes, plasma, and liquid crystal display glass all use rare earth-based polish to shine.
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