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USA (FRL) | |
| Missen, O. P., Back, M. E., Mills, S. J., Roberts, A. C., LePage, Y., Pinch, W. W., & Mandarino, J. A. (2021). Crystal Chemistry of Zemannite-Type Structures: III. Keystoneite, the Ni2+-Analogue of Zemannite, and Ferrotellurite Discredited. The Canadian Mineralogist, 59(2), 355-364. Eckel, Edwin Butt , Cobban, Robert R., Mosburg, Shirley K., Foord, Eugene E. (1997) Minerals of Colorado. Fulcrum Publishing. |
| Eckel, Edwin Butt , Cobban, Robert R., Mosburg, Shirley K., Foord, Eugene E. (1997) Minerals of Colorado. Fulcrum Publishing. |
- La Plata Mining District (California Mining District)
| M.E. Ciriotti, 2006, probed |
Keystone Mine, Magnolia Mining District, Boulder County, Colorado, USA