Tetradymite, montanite

A collection sample of tetradymite from the type locality Župkov in central Slovakia. A rich position full of gray, metallic lustrous crystals of this telluride and bismuth sulfide runs through the entire sample of silicified andesite. Crystals of tetradymite, up to 3 mm in size, are locally coated with pronounced yellow montanite, which is formed by the decomposition of tetradymite.