@misc{indiciae33fa1bc2ee2e,
  title = {A definition of coal; reply},
  author = {James M. Schopf},
  year = {1957},
  doi = {10.2113/gsecongeo.52.5.585},
  url = {https://pubs.usgs.gov/publication/70213492},
  note = {Source identifier: 70213492}
}