Agatized Coral from Tampa Bay, Florida
Contributed by: Michael Crawford
Date: Jun 29th, 2025
Locality: Ballast Point, Tampa Bay, Tampa, Hillsborough County, Florida, USA (See on Mindat)
Size: 7 x 14 cm
Description:
This is a polished end cut of agatized coral from Tampa Bay, Florida. The coral is found in the Tampa Member of the Arcadia Formation of Early Miocene age. The coral originally formed as calcium carbonate (calcite and aragonite). The carbonate was replaced by silica after being buried by younger sediments. The most common fluorescence of these corals are hues of white or bluish white activated by organic compounds. This type of fluorescence is shown in the longwave image. Green fluorescence is uncommon in Tampa Bay agatized coral. The shortwave emission spectrum shows the green fluorescence is activated by the uranyl ion. The uranium may have been leached from phosphate deposits in the Bone Valley Formation that overlie the Arcadia Formation.
I believe the orange fluorescence seen in the shortwave image is dried lubricant used in cutting the coral.
Summary of luminescence responses:
Agatized Coral (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Blue
- Fluorescence under Longwave (365nm LED) UV light: Yellow
- Fluorescence under Shortwave (255nm LED) UV light: Blue
- Fluorescence under Shortwave (255nm LED) UV light: Green