@misc{indiciae0c62b6f655b9,
  title = {Coal resource classification system of the U.S. Geological Survey},
  author = {Gordon H. Wood and Thomas M. Kehn and M. Devereux Carter and William C. Culbertson},
  year = {1983},
  doi = {10.3133/cir891},
  url = {https://pubs.usgs.gov/publication/cir891},
  note = {Source identifier: cir891}
}