Smithsonite after Calcite (SA-004)

specimen number:
9273196

location:
San Antonio Mine, Santa Eulalia, Chihuahua, Mexico

description:

Sharp scalenohedral crystals of what were once calcite measuring to 3.0 cm in size, these covering the top of matrix and replaced by yellow green crystallized translucent smithsonite. In super condition. An outstanding cabinet sized example for one of these Mexican classics.

The San Antonio mine, situated within the East Camp of the famous Santa Eulalia district in Chihuahua, Mexico, is a major historical underground mining operation renowned for its complex polymetallic ore bodies. Geologically, the deposit is classified as a classic high-temperature, carbonate-replacement and skarn system where thick sequences of Cretaceous limestone were intruded by deep-seated Tertiary felsic magmas, triggering intense fracturing and fluid migration. Hydrothermal solutions replaced the host limestone with extensive, massive mantos and vertical chimneys rich in lead, zinc, silver, copper, and iron sulfides, with the San Antonio mine specifically tracking deeply into advanced tin and vanadium-bearing silicate skarn zones at its lowest levels. Organized large-scale exploitation at the San Antonio property began in the early twentieth century, with corporate development accelerating under companies like the American Smelting and Refining Company (Asarco) during the 1920s and 1930s. The mine operated dynamically as a core producer throughout the mid-to-late 1900s, weathering various economic cycles and temporary ownership transitions before industrial-scale extraction slowed and primary commercial operations ceased around the early 2000s.

Pseudomorphs represent a fascinating mineralogical phenomenon where a mineral chemically replaces or crusts over an existing crystal, adopting and preserving the external crystal morphology of the original species while changing its internal composition. In the highly oxidized upper zones of the San Antonio mine, low-temperature, zinc-rich meteoric waters reacted continuously with pre-existing carbonates, resulting in classic pseudomorphs of smithsonite after calcite. During this secondary alteration process, zinc carbonate fluids gradually replaced the calcium carbonate of the original, well-developed calcite crystals, or deposited a thick, botryoidal crust over them before the underlying calcite completely dissolved away. This replacement left behind distinct, sharply formed smithsonite specimens that perfectly mirror the original rhombohedral or scalenohedral shapes of the parent calcite, often displaying the characteristic pearly luster and white, grey, or pale pink coloration typical of the district.

Questions about this specimen?
Send an email or call us: 314-341-1811.