@misc{indiciae6a5be7374b54,
  title = {Modes of occurrence of trace elements in coal},
  author = {Robert B. Finkelman},
  year = {1981},
  doi = {10.3133/ofr8199},
  url = {https://pubs.usgs.gov/publication/ofr8199},
  note = {Source identifier: ofr8199}
}