Tetradymite, montanite

A rare specimen of well-crystallized tetradymite, a sulfotelluride of bismuth, from its Central Slovakian type locality. A sizeable specimen of silicified andesite, whose cavities are sporadically covered on various sides by tetradymite crystals up to 1 mm in size. Dominating the cavity on the display side is a cluster of two two-millimeter, sharply defined, and undamaged tetradymite crystals. Both crystals are coated with a layer of yellow montanite, a rare tellurate of bismuth.