Opal from
USA | |
| Granger, H.C. & Raup, R.B. (1962), USGS Bull. 1147A, Recon. Study of Uranium Deps. in AZ: A16-A18. |
| [var. Fire Opal] Galbraith, F.W. & Brennan (1959), Minerals of AZ: 87. |
| Theodore, T.G., et al (1987), USGS PP 1361: 148-149 (Table 11). |