Fluorite with Hydrocarbon Inclusions - Cave-In-Rock, Illinois

Contributed by: Chris Clemens
minID: 3X9-1LG
Date: May 19th, 2026
Locality: Cave-in-Rock, Cave-In-Rock Mining Sub-District, Hardin County, Illinois, USA (See on Mindat)
Size: 68.8 x 45.2 x 93.7 mm
Weight: 198 g

Description:
Cluster of purple cubic fluorite crystals, from Cave-In-Rock, Hardin County, Illinois. These fluorite cubes show a blue, fluorescent response under all wavelengths of UV light, and also contain hydrocarbon inclusions that fluoresce a bright white color. The numerous, fluorescent hydrocarbon inclusions visible as bright white whisps, clouds, and dots.

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: Blue
• Fluorescence under Midwave (305nm Lamp/Mercury) UV light: Blue
• Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Blue