Sphalerite with Fluorite, Quartz

specimen number:
2212154

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

description:
Lustrous black crystals of sphalerite across both sides of this quartz crystal covered matrix. Small crystals of purple fluorite present as well. Some damage present as seen.

The Davis-Deardorff Mine, located in the Cave-In-Rock District of Hardin County, Illinois, is a significant locality within the Illinois-Kentucky Fluorspar District known for its high-quality sulfide and halide minerals. Geologically, the deposit is a Mississippi Valley-Type (MVT) occurrence where mineralizing fluids replaced Mississippian-age limestone and sandstone layers, particularly within the St. Louis and Ste. Genevieve Formations. The mine is noted for producing sharp, lustrous sphalerite crystals that are frequently associated with clear to milky quartz and colorful fluorite. Historically, the Davis-Deardorff was an active producer of fluorspar and zinc ores, with primary industrial mining and quarrying operations taking place during the mid-20th century, particularly from the 1940s through the 1960s. These operations were part of a larger regional effort to provide essential raw materials for the steel and chemical industries during and after World War II.

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