@misc{indiciaecaf2d6c38dd8,
  title = {Petrography of a sulfur occurrence in the Castile Formation, Southwest Texas},
  author = {B.M. Madsen and O. B. Raup},
  year = {1987},
  doi = {10.3133/ofr87479},
  url = {https://pubs.usgs.gov/publication/ofr87479},
  note = {Source identifier: ofr87479}
}