Fluorite with Calcite

specimen number:
2242025

location:
M.F. Oxford Mine #7, Hardin Co., Illinois, USA

description:
A beautiful cluster of gem quality golden yellow cubic fluorite crystals measuring to 4.0 cm on edge without matrix. Small crystals of calcite are scattered throughout. There are light blue color zones around the edges of the cubic crystals. Some damage present as shown. Quite attractive when backlit as shown in the picture and at the end of the video.

The M.F. Oxford No. 7 Mine, located in the Cave-in-Rock District of Hardin County, Illinois, was a notable producer within the Illinois-Kentucky Fluorspar District. Geologically, the mine exploited stratiform bedding-replacement deposits hosted within Mississippian-aged limestones, specifically targeting the Fredonia and Renault formations where mineralizing fluids were trapped beneath impermeable shale layers. The site is recognized for producing high-quality fluorite, often occurring as sharp, transparent cubic crystals in shades of yellow and purple, frequently found in association with sphalerite and occasionally petroleum inclusions. Historically, mining and quarrying at the Oxford No. 7 began in the mid-20th century, with significant production occurring during the 1960s and 1970s under the operation of the Ozark-Mahoning Company. The mine contributed to the regional output of acid-grade fluorspar required for aluminum and chemical manufacturing until its eventual closure as shallow, high-grade reserves were depleted and market conditions shifted.

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