@misc{indiciae57777a32715c,
  title = {Niobium content of soils from West Africa},
  author = {F. S. Grimaldi and I.A. Berger},
  year = {1961},
  doi = {10.1016/0016-7037(61)90060-6},
  url = {https://pubs.usgs.gov/publication/70009801},
  note = {Source identifier: 70009801}
}