Witherite with Calcite

specimen number:
2133282

location:
Minerva Mine #1, Hardin Co., Illinois, USA

description:
Lustrous translucent colorless pyramidal crystals of witherite in a cluster with spiky crystals of calcite. This is in very good condition; only a couple of the calcite crystals are cleaved. This is typical for calcite in this crystallization habit from the locality. A neat association specimen for this American classic.

The Minerva Number 1 mine, situated near Cave-in-Rock within Hardin County, Illinois, United States, is a historic and globally celebrated mineral locality renowned for producing exceptional industrial fluorite alongside sharply formed, highly significant specimens of the rare barium carbonate mineral witherite. Geologically, this major underground operation targeted stratiform, bedding-replacement deposits hosted within Mississippian-age sedimentary rocks, specifically the Joppa member of the Ste. Genevieve Limestone and the overlying Renault Formation. Intense regional faulting along the Fluorspar District permitted deep-seated, low-temperature hydrothermal fluids to ascend and selectively dissolve the favorable limestone strata, replacing the carbonate rock with massive fluorite, sphalerite, and barite, while late-stage fluid cooling allowed magnificent, white to translucent, pseudohexagonal bipyramidal twins of witherite to crystallize inside open solution cavities and cave pockets. Historically, organized underground development began in March 1942 under the Ozark-Mahoning Company, which sank the main shaft to exploit the extensive ore bodies, supplying vital chemical-grade fluorite and zinc concentrates to domestic industries throughout the mid-to-late twentieth century. The property was subsequently acquired by the Minerva Oil Company and later the Seaforth Mineral and Ore Company, with continuous extraction running until the exhaustion of economic reserves forced the permanent closure and flooding of the underground workings in 1996.

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