@misc{indiciae2e82deac5afd,
  title = {International strategic minerals inventory summary report; niobium (columbium) and tantalum},
  author = {R.N. Crockett and D. M. Sutphin},
  year = {1993},
  doi = {10.3133/cir930m},
  url = {https://pubs.usgs.gov/publication/cir930M},
  note = {Source identifier: cir930M}
}