@misc{indiciaef459a4a26ee1,
  title = {The U.S. Geological Survey coal quality (COALQUAL) database version 3.0},
  author = {Curtis A. Palmer and Charles L. Oman and Andy J. Park and James A. Luppens},
  year = {2015},
  doi = {10.3133/ds975},
  url = {https://pubs.usgs.gov/publication/ds975},
  note = {Source identifier: ds975}
}