Opal from selected localities.
USA | |
| California Geology (1981): 185, figure 2 (September, 1981); USGS MRDS database (2005), loc. file ID #10212662. |
| [var: Fire Opal] Bradley, W.W. (1916a), Colusa, Glenn, Lake, Marin, Napa, Solano, Sonoma, Yolo County: California Mining Bureau. Report 14: 321; Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 282. |
| Honke, Martin T., Jr. & Wm. E. Ver Planck, Jr. (1950), Mines and mineral resources of Sonoma County, California: California Journal of Mines and Geology: 46(1): 94. |