Fluorite on Barite

specimen number:
2013544

location:
Ozark Mahoning #1 Mine, Hardin Co., Illinois, USA

description:
Deep blue lustrous and gemmy crystals of fluorite measuring to 1.7 cm on edge across the top of a barite matrix. In super condition. Collected in the early 1990s.

The Ozark-Mahoning Number 1 Mine, situated in the Cave-in-Rock District of Hardin County, Illinois, is a landmark locality within the Illinois-Kentucky Fluorspar District. Geologically, it is a Mississippi Valley-Type (MVT) deposit where mineralization occurs within the Mississippian-aged Mississippian limestones, particularly the Ste. Genevieve and St. Louis formations. The ore bodies formed as bedding-replacement deposits, known as mantos, when fluorine-rich hydrothermal fluids moved along the Peters Creek Fault system and reacted with the carbonate host rocks. Historically, the mine was a major producer for the Ozark-Mahoning Company, a subsidiary of Pennwalt Corporation, throughout the mid to late 20th century. It served as a vital source of acid-grade fluorspar for the chemical industry until the closure of the district's last mines in the 1990s due to the influx of lower-priced international imports.

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