20 Euros Protected Opalfield - Dubnícke Mines

Issued as part of Slovakia's ongoing natural heritage series, this coin commemorates the opal deposits near Dubník in eastern Slovakia — historically the most significant precious opal source in Europe and, for centuries, the primary supplier to royal courts and gem markets across the continent. Hungarian nobles controlled the mines intensively from the medieval period onward, and the deposit's decline in commercial relevance only accelerated after significant Australian opal discoveries in the late 19th century flooded global supply.

The "protected opalfield" designation reflects Slovakia's formal geological protection of the Dubník site under national heritage law.