Fluorite

specimen number:
2092274

location:
Lead Hill, Hardin Co., Illinois, USA

description:
A cluster of translucent purple cubic fluorite crystals. Some cleaving present. Attractive when backlit as shown in the picture and at the end of the video.

The Lead Hill mining area, situated near Cave-in-Rock in Hardin County, Illinois, was a historically significant upland locality within the Illinois-Kentucky Fluorspar District, known for its shallow fissure-vein and bedding-replacement deposits. Geologically, the site features a series of mineralized structures cutting through Mississippian-age sedimentary formations, particularly the St. Louis Limestone. Hydrothermal fluids migrating through the regional fault systems dissolved the host carbonate rocks and deposited high-grade fluorite, galena, and sphalerite within open fault fissures and collapse breccias, creating pockets that yielded well-crystallized cubic fluorite, typically in shades of yellow and purple, alongside associated sulfide minerals. Historically, Lead Hill was the site of some of the earliest mining efforts in the district, with open-cut quarrying and shallow shaft prospecting for lead ore beginning as early as the 1840s and 1850s. The operations shifted focus heavily toward industrial fluorspar extraction during the late nineteenth and early twentieth centuries, operating via a complex network of small, interconnected surface pits, adits, and shallow underground workings managed by various independent operators and consolidated companies. While intensive, organized commercial mining at Lead Hill largely wound down by the mid-twentieth century as production shifted to deeper, more centralized mechanized shaft mines like the Minerva complex, the locality remained a well-known site for intermittent geological study and localized specimen recovery efforts extending through 2026.

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