Orthoclase (SIL-0009)

specimen number:
9273200

location:
La Valenciana Mine, Guanajuato, Mexico

description:
Often referred to as adularia, these are blocky crystals of a potassium feldspar measuring to almost 3.0 cm on edge in a cluster with matrix. These are sometimes referred to by the varietal name valencianaite. in great condition.

The La Valenciana mine, situated on the northern edge of Guanajuato, Mexico, was one of the most prolific silver-gold mines in global history. Geologically, the deposit is hosted along the Variscan-age Veta Madre (Mother Lode), a major northwest-trending epithermal fault vein system that cuts through Mesozoic metamorphic rocks and Tertiary volcanic sequences. Hydrothermal activity along this fault deposited rich bands of argentite, polybasite, electrum, and native silver within a gangue of quartz and calcite. Formal exploration began in 1760 under Antonio de Obregon y Alcocer, and by 1768, the operation struck a massive bonanza zone, leading to the construction of the iconic Octagonal Shaft (Tiro General). The mine operated continuously at extraordinary capacity through the late eighteenth century, producing a significant percentage of the world's silver, until the Mexican War of Independence disrupted production in 1810. Following periods of flooding and intermittent exploitation by British and American consortia in the nineteenth and twentieth centuries, the mine underwent cooperative local management before transitioning into a protected historic and tourist destination, though localized mining exploration persists in the region today.

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