Não informado. (1964). Commodity Data Summaries. U.S. Department of the Interior, Bureau of Mines.
Chicago-referens (17:e uppl.)Não informado. Commodity Data Summaries. Washington: U.S. Department of the Interior, Bureau of Mines, 1964.
MLA-referens (8:e uppl.)Não informado. Commodity Data Summaries. U.S. Department of the Interior, Bureau of Mines, 1964.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.