@misc{indiciae5d1dd794737b,
  title = {A definition of coal},
  author = {James M. Schopf},
  year = {1956},
  doi = {10.2113/gsecongeo.51.6.521},
  url = {https://pubs.usgs.gov/publication/70216187},
  note = {Source identifier: 70216187}
}