Fluorite with Hydrocarbon Inclusions - Minerva No. 1 Mine, Cave-In-Rock, Illinois

Contributed by: Chris Clemens
minID: 3QA-WXW
Date: May 21st, 2026
Locality: Minerva No. 1 Mine, Ozark-Mahoning group, Cave-In-Rock Mining Sub-District, Hardin County, Illinois, USA (See on Mindat)
Size: 6.2 x 5 x 10.4 cm
Weight: 417 g

Description:
It is not uncommon for fluorite specimens mined from the historic Illinois-Kentucky Fluorspar District to contain bitumen, oil or other hydrocarbon inclusions. Often, these hydrocarbon inclusions will show bright fluorescence under UV, sometimes producing a spectacular luminescent effect. This specimen, collected from the famous Minerva No. 1 Mine (Cave-In-Rock, Hardin County, Illinois), provides a beautiful example of brightly fluorescent hydrocarbon inclusions. Fluorescent hydrocarbon inclusions are seen as bright blue/white dots within the fluorite cubes.

Originally posted by Chris Clemens on Nature's Rainbows in 2021.

Fluorescence under longwave UV light.

Fluorescence under shortwave UV light.

Normal light.

Normal light. Close-up view of main fluorite cube (28 mm on upper edge)

Fluorescence under longwave UV light. Close-up view of main fluorite cube (28 mm on upper edge)

Fluorescence under shortwave UV light. Close-up view of main fluorite cube (28 mm on upper edge)

Fluorescence under longwave UV light. Close-up 6.8 mm FOV

Fluorescence under shortwave UV light. Close-up 6.8 mm FOV.

Summary of luminescence responses:

Fluorite (Mindat) (RRUFF)

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