@misc{indiciae08af88aee0b9,
  title = {Concentrations of platinum group elements in 122 U.S. coal samples},
  author = {C.L. Oman and R. B. Finkelman and S.J. Tewalt},
  year = {1997},
  doi = {10.3133/ofr9753},
  url = {https://pubs.usgs.gov/publication/ofr9753},
  note = {Source identifier: ofr9753}
}