United States. Bureau of Mines. Mineral Facts and Problems: 1960 Edition. Washington D.C.. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc38790/. Accessed May 3, 2016.
Note: Inconsistencies in capitalization and punctuation within the Digital Library may affect this citation. Before using this citation in formal writing, please consult your preferred style manual. More information.