TY  - RPRT
TI  - Preliminary map of columbium (niobium) and tantalum provinces in the conterminous United States
AU  - Edwin Wilson Tooker
AU  - Raymond Laurence Parker
PY  - 1980
DO  - 10.3133/ofr79576n
UR  - https://pubs.usgs.gov/publication/ofr79576N
ID  - ofr79576N
ER  -