This is a fluorescent, Pliocene age (approx. 5 mya) Mercenaria permagna clam fossil from the famous Rucks' Pit site in Fort Drum, Florida. During the fossilization process of these clams, the calcium carbonate from the original shell material dissolved and recrystalized as beautiful, honey-colored, scalenohedral, calcite crystals on the interior of the shell. The resulting calcite is brightly fluorescent under all wavelengths of UV, and also displays a short-lived green phosphorescence. The exterior of the shell is encrusted with the coquina from which it was removed. The size of this specimen is 94.2 x 79.5 x 47.9 mm, and it weighs 164 grams.