Fluorite with Calcite

specimen number:
2013531

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

description:

A gorgeous cluster of blue cubic gemmy fluorite crystals measuring to 3.0 cm on edge with minor calcite and barite. Very slight chipping present, this still in very good condition. The color is outstanding. Collected in the 1970s.

The Minerva Number 1 Mine is located in the Cave-in-Rock District of Hardin County, Illinois, and represents one of the most significant localities within the Illinois-Kentucky Fluorspar District. Geologically, it is a classic Mississippi Valley-Type (MVT) deposit hosted within the Mississippian-aged St. Louis and Ste. Genevieve Limestones. The mineralization occurred when fluorine-rich hydrothermal brines migrated through the regional fault systems, reacting with the carbonate host rocks to deposit minerals in large, open solution cavities and bedding-replacements. Historically, the mine began operations in the early 1940s and remained a primary producer of acid-grade fluorspar for decades. It was a cornerstone of the regional economy until the late 20th century, with the mine finally closing in 1996 as the domestic fluorspar industry declined due to global competition.

For mineral collectors, Minerva Number 1 is world renowned for producing some of the finest fluorite specimens ever discovered. The crystals are famous for their remarkable color zoning, often featuring nested cubes of yellow, purple, and blue within a single transparent crystal. These cubes are frequently found in aesthetic association with brassy chalcopyrite, lustrous sphalerite, bladed barite, and sharp calcite crystals. The mine is particularly noted for its large, museum-quality plates where lustrous, multi-colored fluorite cubes sit atop a matrix of limestone or associated sulfides. Because the mine is now flooded and inaccessible, specimens from the historic workings have become highly sought-after classics, representing the pinnacle of American fluorite mineralization and a golden era of Midwestern mining history.

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