@misc{indiciae58fed66de6d1,
  title = {Niobium and tantalum},
  author = {Klaus J. Schulz and Nadine M. Piatak and John F. Papp},
  year = {2017},
  doi = {10.3133/pp1802m},
  url = {https://pubs.usgs.gov/publication/pp1802M},
  note = {Source identifier: pp1802M}
}