Fluorite with Calcite

specimen number:
2292450

location:
Southern Illinois Fluorspar District, Illinois, USA

description:
A large crystallized point of lustrous translucent fluorite crystals, the backside covered with sparkling colorless crystals of calcite. In good condition all around.

The Southern Illinois Fluorspar District, located primarily in Hardin and Pope counties, is geologically significant for its Mississippi Valley-Type (MVT) deposits. These fluorite (fluorspar) deposits formed in the Mississippian-age limestone and sandstone layers through hydrothermal activity, where mineral-rich fluids traveled along faults and fractures to precipitate calcium fluoride. Mining in this region began in the early 19th century, with significant commercial production starting in the 1870s to supply the steel and chemical industries. The district became a dominant source of domestic fluorspar for the United States for over a century. Beyond its industrial use, the area is historically noted by mineral collectors for producing specimens of fluorite featuring diverse colors and crystal forms, often associated with minerals such as calcite, galena, and sphalerite, recovered throughout decades of active underground mining.

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