There is no disputing the world-class quality of the Bournonite crystals found at Viboras mine in Potosí Department, Bolivia. Their form, as classic 'cog-wheels' is remarkable, with such perfection and sharpness of crystal faces and bright gunmetal grey colour and metallic lustre. These crystals can also reach exceptional sizes, but this miniature-sized specimen is more modest, with crystals to 1.7 cm across. Nevertheless, these are amazing crystals for the species, freestanding and in exceptional condition. Associated with them are the inconspicuous "Freibergite" reported from the mine. Freibergite has since been discredited as an individual species - split into a range of silver-bearing 'Tetrahedrites' but the specific identify of these Viboras Argentotetrahedrites is not known.
