Root Beer Fluorite and Celestine from Clay Center, Ohio
Contributed by: Michael Crawford
Date: Jul 19th, 2025
Locality: Clay Center, Allen Township, Ottawa County, Ohio, USA (See on Mindat)
Size: 9 x 12 cm
Description:
This specimen features root beer fluorite cubes alongside celestine crystals from Clay Center, Ottawa County, Ohio. The crystals developed within vugs of Silurian-age Lockport Dolomite. Fluorite cubes reach sizes up to 4 cm, with their characteristic brown coloration resulting from microscopic hydrocarbon inclusions, which also activate a bluish-white fluorescence. The fluorite exhibits fluorescence under all wavelengths of ultraviolet (UV) light, and the fluorescence reveals distinct zoning patterns. The fluorescence primarily emanates from the brown interior of the fluorite cubes, while the clear edges display reduced fluorescent intensity. Celestine crystals, in contrast, exhibit blue-white fluorescence under longwave UV illumination.
Analysis of the emission spectra indicates that the peak fluorescence wavelength of fluorite shifts from 447 nm under longwave UV to 433 nm under shortwave UV, resulting in a perceptibly bluer hue under shortwave conditions. The spectral peak of celestine emission is significantly narrower than that of fluorite emission, producing a pronounced blue fluorescence, whereas the broader fluorite peak combines multiple colors to create a white appearance.
Following UV exposure, the fluorescence afterglow differs depending on the wavelength of illumination. Exposure to longwave UV produces a green afterglow, while exposure to shortwave UV results in a blue-white afterglow.
Summary of luminescence responses:
Fluorite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: White
- Fluorescence under Midwave (305nm LED) UV light: White
- Fluorescence under Shortwave (255nm LED) UV light: White
- Fluorescence under Longwave (365nm LED) UV light: Blue