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 April 18, 2015.
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.