@misc{indiciae013df80625c9,
  title = {Natural gemstones},
  author = {Members of the Engineering Geology and Ground Water Branches, U.S. Geological Survey},
  year = {2001},
  doi = {10.3133/7000030},
  url = {https://pubs.usgs.gov/publication/7000030},
  note = {Source identifier: 7000030}
}