Fluorite with Calcite

specimen number:
2092272

location:
Denton Mine, Hardin Co., Illinois, USA

description:
Lustrous translucent amber colored scalenohedral crystals of calcite to 3.5 cm in size in a cluster with purple crystals of fluorite measuring to 3.0 cm in size. Some damage present, still a nice combination piece.

The Denton mine, situated in the Harris Creek mining sub-district of Hardin County, Illinois, was a major underground operation within the historic Illinois-Kentucky Fluorspar District. Geologically, the deposit is characterized as a Mississippi Valley-type (MVT) stratiform, bedding-replacement ore system hosted within Mississippian-age sedimentary carbonate formations, particularly the limestone beds at the Rosiclare and Sub-Rosiclare horizons. Low-temperature, metal-bearing hydrothermal fluids migrating through regional fault zones dissolved specific limestone layers and precipitated mineralized beds, forming expansive cavity networks that produced exceptional cubic fluorite crystals, often showing sharp purple or yellow zoning, along with massive glassy chalcopyrite-coated calcite scalenohedrons, galena, sphalerite, and baryte. Historically, underground shaft development and room-and-pillar extraction began at the site in late 1979 under the direction of the Ozark-Mahoning Company, with the main shaft reaching commercial output levels in 1981. The facility operated as a highly productive industrial center, extracting substantial quantities of metallurgical and acid-grade fluorspar alongside byproduct lead and zinc until global economic pressures, coupled with high underground operating costs and cheaper foreign imports, led to the progressive winding down of operations and the formal cessation of mining at the Denton property in 1993.

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