Calcite with Sphalerite, Quartz

specimen number:
2092214

location:
Davis-Deardorff Mine, Hardin Co., Illinois, USA

description:
Lustrous black crystals of sphalerite acting as a matrix for crystallized calcite and quartz. Minimal damage present. Nice old timer.

The Davis-Deardorff Mine, situated near Rosiclare in Hardin County, Illinois, was a key producer within the Illinois-Kentucky Fluorspar District. Geologically, the mine exploited bedded-replacement deposits where mineral-rich hydrothermal fluids replaced specific limestone layers within the Mississippian-aged Downeys Bluff and Bethel formations. The ore body was characterized by high-grade fluorite, often occurring in massive crystalline forms or as well-developed cubes, frequently associated with minerals like sphalerite, galena, and calcite. Historically, the mine was operated by the Ozark-Mahoning Company, with significant production occurring throughout the mid-20th century, particularly during the 1940s and 1950s when demand for fluorspar in steel and chemical manufacturing was at its peak. Access to the underground workings was primarily through the Davis shaft, and the mine was noted for its efficient extraction of the relatively flat-lying ore bodies. While large-scale mining at the site eventually ceased as local reserves were depleted and global market conditions shifted, the Davis-Deardorff remains a significant name in the history of Illinois mining for its contribution to the nation's industrial mineral supply.

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