Clausthalite with Calcite

Clausthalite is a rare lead selenide (PbSe) and on this small cabinet specimen forms granular metallic patches sparsely distributed through a massive milky white Calcite matrix.  The largest patch of Clausthalite measures 7 x 3 mm and all occurrences are metallic black, often with a slight iridescent blue sheen.  The Calcite surrounding the Clausthalite is partly crystallised, displaying occasional prism faces.  The Calcite covers the top surface of a black and earthy carmine basaltic looking matrix.  A rather lovely old German label accompanies this specimen, written in a beautiful, yet now somewhat faint, copperplate hand.