Fluorite (O-090)

specimen number:
9273205

location:
Ojuela Mine, Mapimi, Durango, Mexico

description:

Beautiful gemmy purple crystals of lustrous fluorite measuring to 1.5 cm in size across the front of matrix. In great condition. Very choice for the species at this locality.

The Ojuela mine, located near Mapimi in the state of Durango, Mexico, is a world-famous underground mining operation legendary for its spectacular karst-associated oxidation zone that has produced over one hundred and forty distinct mineral species, including magnificent collector specimens of adamite, legrandite, and hemimorphite. Geologically, the deposit is a premier example of a carbonate replacement system, where high-temperature polymetallic hydrothermal fluids associated with Tertiary-age igneous intrusions replaced thick Cretaceous-age Aurora Limestone beds along structural intersections, regional faults, and solution collapse breccias. Deep, prolonged supergene weathering subsequently oxidized the primary galena, sphalerite, and arsenopyrite ores down to a depth of over five hundred meters, creating an intricate network of mineral-lined caves and pockets rich in secondary lead, zinc, copper, and arsenic compounds. Historically, Spanish explorers discovered the rich outcroppings in 1598, initiating centuries of intermittent silver, gold, and lead mining that culminated in large-scale corporate industrialization under the Compania Minera de Penoles starting in 1888. Penoles constructed a massive underground complex involving over one hundred miles of tunnels and erected the historic, three hundred-meter-long Puente de Ojuela suspension bridge in 1892 to transport ore across a deep canyon to the Mapimi smelter. Regular corporate underground extraction for industrial base metals operated continuously until rising water levels and ore depletion forced the cessation of large-scale corporate operations in 1932, after which the mine was turned over to local miner cooperatives (mineritos) who continue selective manual mining to extract pristine crystal specimens for the global collector market through 2026.

Plattnerite is a heavy lead dioxide mineral that crystallizes in the tetragonal system, typically forming as a secondary alteration product within the deeply oxidized zones of lead-bearing hydrothermal ore deposits. Geologically, it develops through the weathering and oxidation of primary lead minerals, most notably galena, under highly oxidizing, alkaline chemical conditions near the surface. The mineral is visually distinctive, characteristically occurring as dark iron-black to brownish-black velvety crusts, nodular masses, or minute prismatic crystals that exhibit a brilliant submetallic to adamantine luster. Because of its specific chemical stability, it frequently occurs in association with other secondary lead species like cerussite, pyromorphite, and wulfenite, serving as a key indicator of highly developed supergene oxidation zones within lead-rich geological environments.

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