Fluorite with Calcite

specimen number:
2092227

location:
Southern Illinois Fluorspar District, Illinois, USA

description:

Purple cubic crystals of fluorite lustrous in measuring to 3.0 cm on edge across the top of matrix. Minor calcite present. Slight damage present, still quite nice.

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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