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Known Atom in the Universe. New York: Black Dog & Leventhal, 2009. Print.
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n.d. Web. 03 Dec. 2013.
"Yttrium." Chemicool Periodic Table. Chemicool.com. 18 Oct. 2012. Web. 12/4/2013
<http://www.chemicool.com/elements/yttrium.html>.