@misc{indiciae39e25fd58c9c,
  title = {Field determination of microgram quantities of niobium in rocks},
  author = {F. N. Ward and A. P. Marranzino},
  year = {2002},
  doi = {10.1021/ac60104a034},
  url = {https://pubs.usgs.gov/publication/70011003},
  note = {Source identifier: 70011003}
}