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Dysprosium is a chemical element with the symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster.
D 5670 (OTTO) Dysprosium foil, 0.50 mm, thick, 99.99% Cas 7429-91-6 - used for magnets, and as a poison in nuclear reactors where it stops the reaction from getting out of hand. The abundance in the Earth's crust of dysprosium is 6 ppm.