Smithsonite after Calcite (O-0045)

specimen number:
9273212

location:
Ojuela Mine, Mapimi, Durango, Mexico

description:

A cluster of what were once scalenohedral crystals of calcite measuring to 4.5 cm in size, these now replaced by crystallized smithsonite. In great condition.

The Ojuela mine, located near Mapimi in Durango, Mexico, is a world-famous underground deposit renowned for its exceptional variety of secondary arsenate minerals. Geologically, the site is a major carbonate replacement deposit hosted within the thick Cretaceous-aged Cupido and Aurora Limestones. Mineralization occurred when high-temperature, metal-rich hydrothermal fluids ascended along major structural faults, dissolving the limestone and replacing it with massive lead, zinc, and silver sulfides, which were later subjected to intense, deep-seated oxidation that formed a complex suite of secondary minerals in open cavities. Underground commercial extraction began shortly after its discovery in 1598, with production reaching an industrial scale in the late nineteenth century under the management of the Compania Minera de Penoles, which constructed an extensive infrastructure including a famous suspension bridge. Primary corporate mining for industrial ores declined and officially ceased in the late 1940s, after which the mine transitioned into a highly organized, artisanal specimen-mining operation that continues to supply the international mineral market into the twenty-first century.

The mine is also celebrated for its unique pseudomorphs, most notably sharp smithsonite after calcite specimens. In these occurrences, zinc-rich meteoric waters slowly dissolved the original rhombohedral calcite crystals while simultaneously precipitating smithsonite, perfectly preserving the original crystal habit as a chemical replacement.

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