Fluorite

specimen number:
2092270

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

description:
Light blue lustrous and gemmy cubic crystals of fluorite measuring to 2.5 cm on edge forming a matrix less cluster. Very slight micro-chipping present as seen. Crystallized naturally all around. Attractive when backlit as seen in the picture and at the end of the video.

The Minerva Mine Number 1, situated near Cave-in-Rock in Hardin County, Illinois, was one of the largest and most technologically advanced underground operations within the historic Illinois-Kentucky Fluorspar District. Geologically, the deposit is a premier example of a stratiform, bedding-replacement (manto) system hosted within Mississippian-age sedimentary rocks, specifically the limestones of the Renault and Ste. Genevieve Formations. Low-temperature, metal-bearing hydrothermal solutions migrated along major regional fault structures, dissolving the carbonate beds and precipitating thick, stratified layers of high-grade fluorite, creating immense cavernous pockets that produced spectacular cubic crystals in vibrant shades of yellow, purple, and blue, frequently associated with sphalerite, galena, barite, and unique scalenohedral calcite groupings. Historically, underground shaft development and room-and-pillar extraction began at the site in 1942 under the Minerva Oil Company, which constructed a major flotation mill to process fluorspar alongside byproduct zinc and lead. The facility operated as a cornerstone of the domestic mining industry for over five decades, later passing to the Ozark-Mahoning Company in the 1970s, until severe economic competition from cheaper international imports and the depletion of easily accessible reserves forced the permanent cessation of all mining and milling operations at the Minerva Number 1 property in 1995.

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