Slovakia FDC on "Slovak Minerals - Precious Opal from Dubnik"

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Slovakia

Slovak Minerals - Precious Opal from Dubnik

Date of Issue : 11 October 2013

Opal is an amorphous substance, hydrated silicon dioxide (SiO2.nH2O), with a variable amount of water (3-21%). Opal can be found in fillings of fissures in Late Tertiary volcanic rocks – andesites in areas between Červenica and Dubník in Slanské vrchy Hills.

A crystal filling of fissure in basalt – aragonite from the area of Bulhary near Fiľakovo in southern Slovakia is depicted on FDC. And a crystalline structure of libethenite – secondary phosphate of copper from Ľubietová, which is one of the 19 Slovak minerals first found and noted down in Slovakia, represents a motif of the FDC cancellation.