Rare Fluorite from the Crystal Mine, Cave-In-Rock, Hardin County, Illinois
Contributed by: Chris Clemens
minID: 829-GLT
Date: Apr 15th, 2026
Locality: Crystal Mine, Cave-In-Rock Mining Sub-District, Hardin County, Illinois, USA (See on Mindat)
Size: 10.8 x 2.8 x 10.9 cm
Weight: 333 g
Description:
The Crystal Mine, one of many fluorspar mines in the historic Cave-In-Rock mining district of Southern Illinois, is not a well-known location for the production of fluorescent mineral specimens. The mine itself shut down production in the 1970s, and specimens from this location are generally quite rare. The Crystal Mine specimen featured here found its way into my collection only recently, and represents a very uncommon Southern Illinois mine location, and as an added bonus, shows a pleasing fluorescent response under UV. This piece consists of a double-sided plate of intergrown, translucent, pale purple fluorite cubes with several colorless calcite scalenohedrons and druse. This specimen displays best under midwave and longwave UV and shows only dim fluorescence under shortwave UV.
This specimen shows its brightest fluorescent response under longwave UV (365 nm). The fluorite cubes produce a beautiful blue glow while intermittent calcite crystals and druse show a white to pale orange response. The midwave UV response of the fluorite is more purple.
Originally posted by Chris Clemens on Nature's Rainbows in 2023.
Summary of luminescence responses:
Fluorite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Blue
- Fluorescence under Midwave (305nm Lamp/Mercury) UV light: Blue
- Fluorescence under Longwave (365nm LED) UV light: Orange