This pair of yellow fluorite cubes from Cave-In-Rock, Hardin County, Illinois, show a very interesting multi-wave fluorescent response due to the presence of wispy hydrocarbon (petroleum) inclusions within the fluorite crystals. Under all wavelengths, the hydrocarbon inclusions show a bright, filamentous, web-like pattern of white fluorescence. Hydrocarbon inclusions are common in fluorite from the Illinois - Kentucky Fluorspar District. The size of this specimen is 63 x 54 x 56 mm, and it weighs 224 grams.
Fluorescence under long wave UV (365 nm).
Fluorescence under mid wave UV (302 nm).
Fluorescence under short wave UV (254 nm).
Under visible light, the fluorite cubes show a vivid yellow color with a pale purple secondary fluorite overgrowth.