@misc{indiciae4a0bf11e16e3,
  title = {Birnessite (delta MnO2-3H2O) in a large spherulite in obsidian near Silver Cliff, Colorado},
  author = {Fred A. Hildebrand},
  year = {1974},
  url = {https://pubs.usgs.gov/publication/70232482},
  note = {Source identifier: 70232482}
}