Fluorite, Calcite and Hydrozincite; Minerva No. 1 Mine, Cave-In-Rock, Illinois
Contributed by: Chris Clemens
minID: 37L-T3Y
Date: Apr 21st, 2026
Locality: Minerva No. 1 Mine, Ozark-Mahoning group, Cave-In-Rock Mining Sub-District, Hardin County, Illinois, USA (See on Mindat)
Size: 68 x 51 x 88 mm
Weight: 371 g
Description:
This beautiful multi-colored fluorescent specimen was surface collected from the tailings that remain at the site of the former Minerva No. 1 Mine, in Cave-In-Rock, Hardin County, Illinois. This rock contains mottled areas of pale purple, white and yellow fluorite and a distinct white vein of calcite running diagonally through the upper third of the rock. The post-mining hydrozincite can be seen as a patchy white coating.
Under shortwave UV (254nm), the fluorite shows a cream/white response, with bright white streaks, clouds and dots of hydrocarbons. Veins of calcite fluoresce pink, red and orange, and numerous patches of post-mining deposited hydrozincite glow bright sky blue.
Under longwave UV (365nm), the fluorite shows a more purple response, while the calcite fluoresces a pale, pastel pink/purple color. The hydrozincite is only dimly fluorescent and shows a dull grey-blue response. The areas of orange fluorescence may be indicative of sphalerite.
Historically, the Minerva No. 1 mine exploited the largest bedding replacement orebody in the United States and operated from the early 1940s until 1996. It changed ownership several times and was a producer of both fluorspar and zinc. Today, little remains of the Minerva other than its tailings.
Originally posted by Chris Clemens on Nature's Rainbows in 2019.
Summary of luminescence responses:
Fluorite (Mindat) (RRUFF)
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Yellow
- Fluorescence under Longwave (365nm LED) UV light: Yellow
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Pink
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Blue