Fluorite

specimen number:
2013626

location:
White Rock Quarry, Clay Center, Ohio, USA

description:

Gorgeous iridescent lustrous crystals of fluorite to 1.0 cm on edge covering the top of matrix with minor calcite and Celestine. While such fluorite is well-known from the Auglaize Quarry, this is quite unusual and rare at this locality. This one is in excellent condition.

The White Rock Quarry, located near Custar in Wood County, Ohio, is a prominent limestone operation known for its contribution to the regional construction industry and its distinct mineralogy. Geologically, the quarry exploits the Middle Devonian Dundee Limestone, a carbonate unit within the Michigan Basin that contains numerous vugs and cavities formed by the dissolution of prehistoric marine life. Historically, the quarry began operations in the mid-20th century and has been a steady producer of crushed stone, aggregate, and agricultural lime for several decades under various owners, including the White Rock Quarry Company. While its primary function is industrial, the site has earned a reputation among collectors for producing unique specimens of calcite, celestine, and fluorite, specifically during active mining phases from the 1970s through the early 2000s.

Iridescent fluorite from here was never common. This optical phenomenon is caused by thin-film interference, where a microscopically thin layer of secondary minerals or hydrocarbons has coated the surface of the fluorite crystals. When light strikes this transparent or translucent film, it reflects off both the outer surface of the coating and the inner surface where the coating meets the fluorite, creating a colorful "oil-on-water" effect. Most frequently, this iridescence manifests as vibrant shades of purple, blue, and gold on the faces of brown or amber-colored cubic crystals. This decorative tarnish is highly valued by collectors, as it enhances the visual appeal of the otherwise dark, petroleum-rich fluorite that characterizes this specific pocket of the Michigan Basin.

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