Opal-CT from
Hungary | |
| Society of Economic Geologists Student Chapter University of Miskolc (2018) Short course – Industrial minerals in the NE part of Hungary. Telkibánya November 5–8. 2018. |
Slovakia | |
| Rusinová P. & Bačík P. (2013): Štruktúrna charakteristika opálu na lokalite Jovsa (Vihorlat). Esemestník, 2, 1, 17-21. |