@misc{indiciae9cd377162c4f,
  title = {Trace elemental analysis of bituminuos coals using the Heidelberg proton microprobe},
  author = {J.R. Chen and H. Kneis and B. Martin and R. Nobiling and K. Traxel and E. C. T. Chao and J.A. Minkin},
  year = {1981},
  doi = {10.1016/0029-554x(81)90598-x},
  url = {https://pubs.usgs.gov/publication/70011884},
  note = {Source identifier: 70011884}
}