Fluorite

specimen number:
8311498

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

description:
Gemmy crystals of purple fluorite to almost 2.0 cm in size across the top of a colorless cubic crystallized fluorite matrix. In good condition with very minimal micro-cleaving present.

The Lead Hill locality, situated near the village of Cave-In-Rock within Hardin County in southern Illinois, United States, represents a highly classic mining area positioned on a prominent knoll at the southwest end of the celebrated Illinois-Kentucky Fluorspar District. Geologically, this area consists of Mississippi Valley-type (MVT) stratiform and bedded replacement deposits, where lower-temperature hydrothermal fluids containing calcium, fluorine, lead, and zinc migrated through structural faults and dissolved highly receptive horizons within Mississippian-age sedimentary rocks, primarily the Fredonia Limestone Member of the Ste. Genevieve Formation and the overlying Renault Formation. The mineralization crystallized along flat-lying bedding planes, creating extensive tabular mineralized bodies filled with distinct cubic fluorite, scalenohedral calcite, galena, sphalerite, and minor chalcopyrite within large solution vugs. Historically, the outcrop workings on Lead Hill are recognized as the cradle of the southern Illinois fluorspar industry, with regional miners first exploiting shallow surficial pockets for lead-bearing galena as early as the 1830s, while discarding the abundant fluorite gangue until new steel-smelting technologies ignited a massive industrial demand for fluorite flux in the late 1880s. A cluster of interconnected underground operations, including the Lead Hill, Robinson, Oxford, and Miller properties, operated intermittently under various corporate and independent lessees for over a century, producing thousands of tons of commercial metallurgical-grade ore until major consolidated underground extraction across the immediate hill area largely phased out by the mid-twentieth century. Through 2026, while historical large-scale industrial shafts across the knoll have long been abandoned, localized open-pit limestone quarrying at the adjoining Hastie properties has periodically breached historical underground voids, occasionally allowing modern geologists and regional collectors to recover unique phantom fluorite specimens that continue to serve as an important academic benchmark for evaluating multi-stage mid-continent hydrothermal mineralization.

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