Fluorite (cleavage octahedron)

specimen number:
8311524

location:
Southern Illinois Fluorspar District, Illinois, USA

description:
A sharp polished cleavage octahedral fluorite, this gemmy and showing inclusions of chalcopyrite. The size provided measures from point to point.

The Southern Illinois Fluorspar District, spanning Hardin and Pope counties centered around Rosiclare and Cave-In-Rock, is a historically monumental mining region where fluorite cleavage octahedrons were produced as a famous local folk-art craft alongside major industrial operations. Geologically, this prolific district consists of Mississippian-age limestone and sandstone formations that were heavily fractured by faulting and subsequently mineralized by low-temperature, mantle-derived hydrothermal fluids, creating massive, high-grade vein and stratiform replacement deposits of dense fluorite. Because fluorite possesses perfect octahedral cleavage along the (111) crystal planes, local miners and collectors discovered they could use a sharp knife blade and a light tap with a small hammer to split large, massive blocks of the mineral along these natural planes of weakness, shaping raw chunks into sharp, smooth, eight-sided double pyramids. Historically, commercial extraction in the district began in 1842 and boomed continuously through the twentieth century to supply the domestic steel and chemical industries, with the production of these hand-cleaved octahedrons flourishing as a prized sideline trade passed down through generations of mining families. Large-scale mining came to an end in the region when the Ozark-Mahoning Company closed the final operating underground mines in early 1996 due to foreign competition, completely halting the influx of fresh material.

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