This is a fluorescent, Pleistocene age (approx. 1-2 Ma) Busycon rucksorum whelk fossil from the famous Rucks' Pit site in Fort Drum, Florida. These fossils occur in the Fort Drum Member of the Nashua Formation, which is exposed in Ruck's Pit in Okeechobee County. Rucks' Pit is best known for producing clam fossils of the species Mercenaria permagna, which often feature beautifully crystallized scalenohedral calcite. During the fossilization process of these gastropods, the calcium carbonate from the original shell material dissolved and recrystalized as light tan to honey-colored calcite. The resulting calcite is brightly fluorescent under all wavelengths of UV, and also displays a short-lived phosphorescence. The shell is encrusted with small amounts of the coquina from which it was removed. The size of this specimen is 64.1 x 39.0 x 32.5 mm, and it weighs 51 grams.
The above image shows the Busycon rucksorum fossil under long wave UV (365 nm). The fluorescence of the calcite-replaced shell is a cream/white color. Note the encrustation of coquina with shell fragments on the right side of the shell.
Green phosphorescence is seen following exposure to long wave UV (365 nm).
As shown above, the fluorescent response under short wave UV (254 nm) is similar to that seen under long wave UV.
Pale blue/green phosphorescence is seen following exposure to short wave UV (254 nm).
Fossil whelk (Busycon rucksorum) shown under visible light. Busycon whelk fossils are less common at Rucks' Pit than the recrystallized Mercenaria clams. The sediments exposed in the Rucks’ Pit were deposited during the late Pliocene and Pleistocene under shallow water near shore conditions.