TY  - RPRT
TI  - A summary of phosphate-rock resources of the United States-an analysis of past estimates
AU  - James Bachelder Cathcart
AU  - Richard Porter Sheldon
AU  - Robert A. Gulbrandsen
PY  - 1981
DO  - 10.3133/ofr81789
UR  - https://pubs.usgs.gov/publication/ofr81789
ID  - ofr81789
ER  -