If you have been looking for an example of Bournonite which exemplifies its common name of cogwheel ore, then perhaps this is the specimen for you. From the relatively recent find at the Viboras mine in the district of Machacamarca, Bolivia, this delightful miniature displays individual metallic steel grey Bournonite crystals averaging 1 to 1.5 cm in diameter, stacked on top of one another, yet sufficiently spaced so as to show off the cogwheel habit wonderfully. Between the Bournonite crystals nestle rich drusy clusters of dull black crystalline Freibergite, forming sub-1 mm cubic and modified cubic crystals. Although Freibergite has now been reclassified as a 'supergroup' rather than a specific species, it remains a complex silver-copper-iron-antimony-arsenic sulphosalt. The Viboras mine is a still active small silver mine in the south west of central Bolivia. A terrific specimen of well crystallised Bournonite with Freibergite from the Viboras mine in Bolivia.
