Viboras Mine, Machacamarca, Machacamarca District (Colavi District), Cornelio Saavedra Province, Potosí Department, Bolivia
Over the last 10 years or so, Machacamarca has produced some of the best Bolivian Bournonite specimens ever found. The diversity of habits and superb quality of the crystals that have come out over the years has set this mine apart as one of the premier localities for the species. Most people are familiar with the new Chinese Bournonites on the market, and because Bolivia does not receive nearly as much attention, I want people to know that I have personally handled some of the finest Bournonite specimens from any locality in the Western Hemisphere that came from this mine. One of the most classic habits for Bournonite is the so called "cogwheel" form that occurs when crystals are twinned along the "m" prism face of crystals. Some of the most well known examples of this habit were found at the Herodsfoot mine in St Just and Wheal Boys mine in Endellion, Cornwall, England. This piece is a highly aesthetic specimen showing the classic "cogwheel" twinning with great reentrant angles between the "cogs". The piece is has a charming, bright gun metal luster and is complete 3/4 of the way around. It is in amazing fine condition, and with so many of the Chinese "cogwheels" on the market (most of which are riddled with damage hosting very high prices), this piece is an apparent bargain for the size and quality. A great thumbnail sized specimen from this lesser recognized Bolivian locality.
Reference:Bourn Bol 5071