Fort Drum, Florida is the only place known for its fossil shells containing crystals.
In the Pliocene and Pleistocene, it was underpinned by the now smaller Lake Okeechobee. Vast deposits of limestone containing the remains of large bivalve molluscs developed calcite crystallization while still underwater. The gemstone-like crystals were discovered after hard limestone deposits were excavated for aggregates. In 2008, the quarry known as Ruck's Pit was closed and allowed to be flooded.