@misc{indiciae815d7724adee,
  title = {U.S. Geological Survey coal quality (COALQUAL) database: Version 2.0},
  author = {L. J. Bragg and J. K. Oman and S.J. Tewalt and C.L. Oman and N. H. Rega and P. M. Washington and R. B. Finkelman},
  year = {1997},
  doi = {10.3133/ofr97134},
  url = {https://pubs.usgs.gov/publication/ofr97134},
  note = {Source identifier: ofr97134}
}