@misc{indiciaec389ec75ebf5,
  title = {Niobium and tantalum: indispensable twins},
  author = {Klaus Schulz and John Papp},
  year = {2014},
  doi = {10.3133/fs20143054},
  url = {https://pubs.usgs.gov/publication/fs20143054},
  note = {Source identifier: fs20143054}
}