@misc{indiciae4be07a16e31b,
  title = {The U.S. Geological Survey coal quality data base (COALQUAL)},
  author = {R. B. Finkelman and C.L. Oman and L. J. Bragg and S.J. Tewalt},
  year = {1994},
  doi = {10.3133/ofr94177},
  url = {https://pubs.usgs.gov/publication/ofr94177},
  note = {Source identifier: ofr94177}
}