Fluorite with Calcite

specimen number:
2292131

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

description:
A cluster of beautiful blue gemmy lustrous crystals of fluorite, the largest 1.5 cm on edge. Small crystals of calcite are sprinkled throughout. Slight damage present, this still in good condition. Crystals of barite are present as well.

The Minerva Mine #1, also known as the Minerva No. 1 mine and later part of the Ozark-Mahoning company holdings, is located near Cave-in-Rock in Hardin County, Illinois, and stands as one of the most significant localities within the Illinois-Kentucky Fluorspar District. Geologically, the deposit consists of bedded replacement ore bodies, classified as Mississippi Valley-Type (MVT) mineralization, hosted within Mississippian-aged sedimentary rocks, particularly the limey layers of the Renault and Ste. Genevieve formations. Hydrothermal fluids migrating along structural faults replaced the native limestone, depositing strata of fluorite, sphalerite, barite, calcite, and galena, which regularly formed open vugs containing sharp, multi-colored cubic fluorite crystals. Underground mining operations at the site commenced around 1942 under the Minerva Oil Company, utilizing room-and-pillar extraction methods to produce metallurgical and acid-grade fluorspar alongside byproduct zinc and lead. The facility ran continuously for decades, changing ownership to the Ozark-Mahoning Company in the 1970s, before permanently closing in late 1995 due to foreign competition and the depletion of easily accessible economic reserves, marking the end of major commercial mining at this specific shaft.

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