Bournonite with Freibergite

If you have been looking for a fine example of Bournonite displaying its famous cogwheel habit to full advantage, then perhaps this specimen is for you.  Mounted vertically on a square clear acrylic base, an excellent Bournonite crystal 2 cm in diameter shows distinct cogwheel teeth all around its circumference and it even meshes with a slightly off-set ‘pinion gear’ to one side.  It might well have been only removed from an unsuspecting gearbox this morning!  From the Viboras mine at Machacamarca in the Potosí Department of Bolivia, Bournonite is a lead-copper sulphosalt (lead-copper antimoniate) and this is partly overgrown by granular, gunmetal-grey crystals of Freibergite, a complex sulphosalt of silver, copper, iron, antimony and arsenic.  A splendid thumbnail of Bolivian Bournonite with Freibergite.