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Fluorite, Calcite and Hydrozincite; Minerva No. 1 Mine, Cave-In-Rock, Illinois

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 hydrocarbon-included fluorite, veins of calcite, and patches of post-mining deposits of hydrozincite. The size of this specimen is 88 x 68 x 51 mm, and it weighs 371 grams.

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.

The above photograph shows the fluorescent response under short wave 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.

Same rock shown under long wave 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.

Visible light photograph of the same specimen, showing 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.

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