International strategic minerals inventory summary report : niobium (columbium) and tantalum - Crockett, R. N.; Sutphin, David M. (Washington : U.S. Government Printing Office, 1993)
Prepared as a cooperative effort among earth-science and mineral-resource agencies of Australia, Canada, the Federal Republic of Germany, the Republic of South Africa, the United Kingdom, and the United States of America
Keywords: Niobium ores; Tantalum ores; Strategic materials