Fluorescent Clam Fossil from Ruck's Pit, Fort Drum, Florida

Contributed by: Chris Clemens
minID: 8G3-WLL
Date: Apr 23rd, 2026
Locality: Rucks\' Pit, Fort Drum, Okeechobee County, Florida, USA (See on Mindat)
Size: 79.5 x 47.9 x 94.2 mm
Weight: 164 g

Description:
This is a fluorescent, Pleistocene age (approx. 1-2 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.

Originally posted by Chris Clemens on Nature's Rainbows in 2016.

Fluorescence under longwave UV light.

Afterglow after exposure to longwave UV light.

Fluorescence under shortwave UV light.

Normal light.

Fluorescence under longwave UV light. Side 2.

Afterglow after exposure to longwave UV light. Side 2.

Fluorescence under shortwave UV light. Side 2

Normal light. Side 2.

Summary of luminescence responses:

Calcite (Mindat) (RRUFF)

• Fluorescence under Longwave (365nm LED) UV light: White
• Afterglow after exposure to Longwave (365nm LED) UV light: Green
• Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: White

• Fluorescence under Longwave (365nm LED) UV light: White