Fluorite with Sphalerite

specimen number:
2013647

location:
Minerva Mine #1, Hardin Co., Illinois, USA

description:
Gorgeous gemmy light blue to yellow cubic crystals of lustrous fluorite across a sphalerite crystal matrix. This is in really good condition.

The Minerva Number 1 mine, situated near Cave-in-Rock in Hardin County, Illinois, is a landmark historical locality within the famous Illinois-Kentucky Fluorspar District. Geologically, the deposit consists of extensive bedded replacement ore bodies and steeply dipping fissure veins hosted within Mississippian-aged sedimentary rocks, specifically the limestones, shales, and sandstones of the Sub-Rosiclare and Renault formations. Mineralization was driven by deep-seated, fluorine-rich hydrothermal fluids rising through structural faults, which reacted with the host carbonate rocks to deposit massive layers of fluorite, sphalerite, galena, and barite, often featuring large mineral pockets lined with highly sharp, multi-colored cubic crystals. Systematic underground development at the Minerva site began in the early 1940s under the Minerva Oil Company to meet critical industrial and wartime demands for metallurgical-grade fluorspar and zinc concentrates. The mine passed through several corporate ownerships, including the Ozark-Mahoning Company in its later decades, and maintained continuous, large-scale production until declining global market prices and competition from cheaper foreign imports forced the permanent closure of the underground workings in 1995.

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