Bournonite

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Choice metallic twinned crystal of bournonite without matrix. Complete all around and in good condition. Good thumbnail for the species.The Viboras Mine, located in the Machacamarca District of Potosi, Bolivia, is a historic mining site renowned for its exceptional sulfosalt mineral specimens. Geologically, the deposit is a complex polymetallic hydrothermal vein system hosted within Silurian sedimentary rocks, which were fractured and mineralized during the Andean Orogeny. The primary ores include tin and silver, with the mine being famous among collectors for its world-class bournonite crystals. The bournonite from this locality typically occurs as brilliant, metallic gray to black "cogwheel" twins, often found in association with quartz, siderite, and pyrite. Historically, the mine saw its most significant period of activity during the mid-20th century, with operations particularly notable between the 1940s and the late 1980s. While large-scale industrial mining has fluctuated with global metal prices, the Viboras Mine remains a legendary name in mineralogy for the sharpness and size of its bournonite specimens, which are considered some of the finest ever recovered from the South American tin-silver belt.