Phosphate Rock Statistics, Historical Statistics for Mineral and Material Commodities in the United States, Data Series 140 US Geological Survey minerals

BUCKINGHAM, D.A. JASINSKI, S.M. (2006): Phosphate Rock Statistics, Historical Statistics for Mineral and Material Commodities in the United States, Data Series 140 US Geological Survey minerals. Reston: U.S Geological Survey URL [Accessed: 20.01.2011]