Wispy Hydrocarbon Inclusions in Fluorite from Cave-In-Rock, Illinois

Contributed by: Chris Clemens
Date: Apr 23rd, 2026
Locality: Cave-in-Rock, Cave-In-Rock Mining Sub-District, Hardin County, Illinois, USA (See on Mindat)
Size: 54 x 56 x 63 mm
Weight: 224 g

Description:
This pair of yellow fluorite cubes from Cave-In-Rock, Hardin County, Illinois, show a very interesting multi-wave fluorescent response due to the presence of wispy hydrocarbon (petroleum) inclusions within the fluorite crystals. Under all wavelengths, the hydrocarbon inclusions show a bright, filamentous, web-like pattern of white fluorescence. Hydrocarbon inclusions are common in fluorite from the Illinois - Kentucky Fluorspar District.

Originally posted by Chris Clemens on Nature's Rainbows in 2016.

Fluorescence under longwave UV light.

Fluorescence under midwave UV light.

Fluorescence under shortwave UV light.

Normal light.

Summary of luminescence responses:

Fluorite (Mindat) (RRUFF)

• Fluorescence under Longwave (365nm LED) UV light: White
• Fluorescence under Midwave (305nm Lamp/Mercury) UV light: White
• Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: White