Calcite with Fluorite

specimen number:
2092234

location:
Southern Illinois Fluorspar District, Illinois, USA

description:
Scalenohedral crystals of calcite across the front of a crystallized fluorite matrix. Some cleaving present, still a nice combination piece.

The Southern Illinois Fluorspar District, spanning Pope and Hardin counties near Rosiclare and Cave-in-Rock, Illinois, United States, was historically the most productive fluorite-mining region in the nation. Geologically, this world-class deposit belongs to the Illinois-Kentucky Fluorspar District and is characterized by Mississippi Valley-type (MVT) mineralization hosted within Mississippian-age sedimentary limestone, sandstone, and shale sequences. Hydrothermal fluids originating from deep-seated igneous intrusions migrated along major northeast-trending faults and structural fractures, precipitating massive vein and stratiform bedding-replacement deposits of exceptionally vibrant fluorite cubes in shades of purple, yellow, and blue, frequently associated with sphalerite, galena, barite, and calcite. Historically, commercial mining began on a small scale in 1842 when miners initially targeted lead-bearing galena near Rosiclare, but the industrial boom exploded in the late nineteenth century as fluorite became crucial as a flux in steelmaking and chemical manufacturing. The district saw intense development during World War I and World War II, boasting massive underground complexes like the Rosiclare, Fairview, and Minerva Number One mines, and it supported a thriving regional economy for over a century. Facing insurmountable economic competition from cheaper foreign imports and declining domestic reserves, the last active underground mine in the district, the Hastie Quarry and Mine complex, permanently ceased all sub-surface fluorspar extraction in December 1995.

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